Abstract: A water or spirit level is composed of an elongated body, preferably of metal, at least one bubble mounted in the elongated body, and end caps, preferably of plastics material, at the end faces of the elongated body, wherein at least one outer surface of the elongated body constitutes a preferred measuring surface. At least one of the end caps is releasably connected to the level body such that the end cap can optionally be removed and once again replaced.

Abstract: An inspection tool for measuring the true of metal door frames uses a plumb bob. The plumb bob is suspended from a holder which may be attached to a door frame by magnets in the body of the holder. The relationship of the holder dimensions models the relationship of the dimensions of a metal door frame. The point indicated by the plumb bob will have the same dimensions from the door frame if the frame is true. If the frame is not true, the point will have different measurements.

Abstract: A device which is attachable to the mast of a forklift for indicating to the forklift operator the tilt angle of the mast in a vertical plane centered on the forklift includes a pivotably supported weighted pendulum, and an elongated activating arm secured to the upper extremity of the pendulum. The activating arm operates a component that is slideably mounted to a base plate, and carries an indicating pointer. A cover member fits over the base plate, and contains a window which accommodates the pointer. Indicia on the cover member interact with the pointer to show the tilt angle of the mast.

Abstract: A multi plane plumb level includes an elongated rigid frame having an X shaped cross section having four walls that are rigidly joined along an elongated central portion of the X shaped cross section and extend outward from the elongated central portion of the X shaped cross section and six level indicating bubble vials that are mounted on front and back sides of the frame in opposing pairs. A pair of flip out transversely oriented bubble vials rotates from secured positions within the front and back sides to extended positions, forming extensions of frame walls to facilitate the leveling of posts, pipes and edges. The remaining two pairs of bubble vials provide level measurements in the longitudinal direction and at a 45 degree angle.

Abstract: A bricklayer's combination level and plumb having a first I-section beam, a second I-section beam, and a connector pivotally and slidably connecting the second I-section beam to the first I-section beam wherein the second I-section is angularly displaceable up to and including a right angle relative to the first I-section beam.

Abstract: An apparatus for indicating correct or faulty back posture comprises a housing and an indicator body. The housing is supported on the user's body. When the user's back posture or head position is incorrect, the indicator body moves and signals the user of the incorrect posture or position, e.g., through an audible alarm.

Abstract: A flexible level is provided that includes a main body comprised of flexible material with bubble devices built in that can be used with the tool in a horizontal (level) or vertical (plumb) positions. The material, when embodied in the configuration of the level, provides 360 degree flexibility in the longitudinal direction, yet rigidity in the other directions. This device has measurement and other features to enhance its use. The full configuration of the device permits one to level and measure around contours of various shaped objects, at interior or exterior corners of structures, and around other various items and places which heretofore required either two people or more complicated devices or tools.

Abstract: A level comprises an extruded thin wall frame structure having an opening of I-shaped configuration extending from end to end thereof. The thin wall frame structure includes a pair of elongated operative walls each having a pair of transversely spaced inwardly turned flanges defining the width thereof and an exterior operative surface extending between the flanges thereof. The operative surfaces are planar and parallel. A pair of angular walls extend from each pair of spaced flanges in converging relation with one another and a pair of central walls are spaced apart in the direction of the width of the operative walls a distance less than the width of the operative walls and integrally interconnected between the pairs of angular walls extending from the flanges. The operative walls and the central walls having a plurality of wall openings therein. An end member closes the opening at each end of the thin wall frame structure.

Abstract: A level comprises an extruded thin wall frame structure having an opening of I-shaped configuration extending from end to end thereof. The thin wall frame structure includes a pair of elongated operative walls each having a pair of transversely spaced inwardly turned flanges defining the width thereof and an exterior operative surface extending between the flanges thereof. The operative surfaces are planar and parallel. A pair of angular walls extend from each pair of spaced flanges in converging relation with one another and a pair of central walls are spaced apart in the direction of the width of the operative walls a distance less than the width of the operative walls and integrally interconnected between the pairs of angular walls extending from the flanges. The operative walls and the central walls having a plurality of wall openings therein. An end member closes the opening at each end of the thin wall frame structure.

Abstract: An aid apparatus for level surveying instrument comprises a housing having a receiving chamber therein, two channels at opposite ends of the receiving chamber respectively, a window at one side of the receiving chamber, and a socket opening at the side wall of the housing connecting to receiving chamber via the channel. A controlling member is slidable received in the housing. The controlling member has a movable bar, two seal block disposed at opposite ends of the movable bar for sealing the channel, and a driving member is provided at the housing for driving the controlling to shift, whereby the sealing block being driven by the driving member to seal the channel and to depart from the channel to prevent bubbles formed in liquid.

Abstract: An extendable carpenter's level which comprises a pair of extending body members capable of adapting and mounting upon the standard “I” level frame configuration of a carpenter's level by sliding said extendable body members onto the frame of the standard level. Each extending body member consists of a top and bottom slide extension rigidly attached to one another so as to be firmly in contact with the level frame. The top and bottom slide he extensions each incorporate a lock pin to insure rigidity as against the level frame and stop clips to eliminate outward extension of the extending body members beyond the end of the level frame. In another embodiment, each extending body member is split such that both the top and bottom slide extensions comprise generally a right and left side extension held together by means of slide springs and flush mounted screws.

Abstract: A door jamb square made of two extensions, a vertical extension and a horizontal extension. Both extensions are provided with bubble spirit levels and are attached forming a right angle, that can be fit into the corner of a door jamb to square that door jamb. The door jamb square is secured to the door jamb using a nailing plate, web plate and a bolt. The web plate is placed within the webbing of the door jamb square, covered by the nailing plate. The web plate and nailing plate each have an aperture aligned and fitted with the bolt. Additional sheetrock screws are used to secure the other side of the nailing plate and door jamb assembly to the door jamb.

Abstract: A water or spirit level is composed of an elongated body, preferably of metal, at least one bubble mounted in the elongated body, and end caps, preferably of plastics material, at the end faces of the elongated body, wherein at least one outer surface of the elongated body constitutes a preferred measuring surface. At least one of the end caps is releasably connected to the level body such that the end cap can optionally be removed and once again replaced.

Abstract: Disclosed are electronic plumb indicators for monopoles, survey poles, global positioning antennas and the like. A exemplary plumb indicator comprises a substrate, a plumb bob suspended by a thread (e.g., wire, cable, string, etc.) and disposed over a first surface of the substrate, and a probe. The substrate has an array of conductive pads disposed over its first surface, preferably in a regular pattern. The probe has a first body portion held by the plumb bob but allowed to move freely in the vertical direction, and a conductive tip disposed between the plumb bob and the first surface of the substrate. The probe tip makes contact with the first surface of the substrate, and contacts one or more pads in normal operation. The pads may be scanned electronically to determine the location of the probe tip and plumb bob with respect to the substrate.

Abstract: A level is composed of a hollow section having two narrow sides, two wide sides and two end faces, wherein at least one of the narrow sides forms a contact surface. The level also includes at least one horizontal bubble and a vertical bubble for carrying out a horizontal and a vertical measurement. The vertical bubble and the horizontal bubble are located outside of the area surrounded by the hollow section and are mounted in side components attached to the end faces of the hollow section.

Abstract: A plumb bob system for allowing an individual to easily utilize a plumb bob in determining whether a wall is plumb. The plumb bob system includes a pole, an engaging structure attached to an upper end of the pole, a pulley rotatably positioned within the engaging structure, a spool containing a length of string passing about the pulley, and a plumb bob attached to the end of the string opposite of the spool. The engaging structure is comprised of a first member and a second member having a first edge and a second edge respectively. The first edge and second edge have a common length of radius from a center point of the pulley to provide an average upper distance (Z) of the string from the wall. The center of the plumb bob has a distance from the lower portion of the wall (X) that is compared to the upper distance (Z). If the upper distance (Z) and the lower distance (X) are equal then the wall is being constructed plumb and no modifications are required in the construction of the wall.

Abstract: A laser plumbing device including a laser beam emitting device; a supporting device for supporting the laser beam emitting device and allowing swinging movements of the laser beam emitting device in a first direction X1 and a second direction Y1; a two-direction drive device for swinging the laser beam emitting device in the first and second directions X1 and Y1; an inclination angle detecting device for detecting an inclination angle of the laser beam emitting direction with respect to the vertical direction; and a controller for controlling the position of the laser beam emitting device by the two-direction drive device so as to change the laser beam emitting direction toward the vertical direction based on the angle detected by the inclination angle detecting device. The long member plumbing device and method utilizing the laser plumbing device.

Abstract: A method for marking a bubble vial, including providing a bubble vial body having an internal cavity for holding therein a fluid, the cavity defining an inner surface of the body, and inking a reference marking on the inner surface.

Abstract: A door jamb square made of two extensions, a vertical extension and a horizontal extension. Both extensions are provided with bubble spirit levels and are attached forming a right angle, that can be fit into the corner of a door jamb to square that door jamb. The door jamb square is secured to the door jamb using a nailing plate, web plate and a bolt. The web plate is placed within the webbing of the door jamb square, covered by the nailing plate. The web plate and nailing plate each have an aperture aligned and fitted with the bolt. Additional sheetrock screws are used to secure the other side of the nailing plate and door jamb assembly to the door jamb.

Abstract: The invention is a new building tool for leveling a flat surface while removing irregularities in the surface by sanding. The tool, named a “rasping level,” integrates into one instrument the functions of leveling and sanding a surface. The rasping level consists of a frame, levels positioned on the top surface of the frame, and sandpaper on the under surface (second surface) of the frame. Along the lengthwise edges of the top surface of the frame are “grippers” for holding and manipulating the tool. The frame and grippers are made of light weight but rigid material. The levels may be typical spirit levels that are used to measure the level and plumb of wall surfaces. Heavy grit sandpaper covers the under surface of the frame. The sandpaper is attached to the under surface of the frame by aerosol adhesive or semipermanent liquid adhesive. Worn-out sandpaper can be removed and replaced by fresh sandpaper as needed.

Abstract: A screed system for walls for allowing the user to work faster and more efficiently and to effectively plaster a wall to a uniform thickness. The screed system for walls includes a mounting bracket being adapted to removably mount to a wall; and also includes a leveling assembly being movably mounted to the mounting bracket and including a leveling tool; and further includes a squaring level assembly being adapted to be mounted in a corner of two adjoining walls; and also includes ia plurality of screed support members being adapted to be fastened to and extended outwardly from studs supporting the wall; and further includes screed members being securely mounted to the screed support members for determining a depth of plaster and mortar being applied to the wall.

Abstract: A slope block assembly having a bubble level with an eccentrically mounted slope block detachably carried on one end of the level. The slope block has an offset turning axis with a plurality of supporting surfaces, all located at different distances from the turning axis. The support surfaces cooperate with an undersurface or support point on the level to direct a laser beam at a desired angle with respect to a round or flat reference surface. Grooves are provided on the slope block support surfaces as well as on the level undersurface to support the level and slope block assembly on a round or curved reference surface.

Abstract: A spirit level including a body having a level face for setting a surface and a non-setting face extending away from said level face, at least one bubble vial mounted in the body, and at least one hand-grip aperture, defining an inner perimeter, formed in the body and which extends through the non-setting face, characterized by the perimeter of the at least one hand-grip aperture being at least partially coated with an elastomer.

Abstract: Position detectors, welding system position detectors, methods of detecting various positions, and methods of providing position detectors are described. In one embodiment, a welding system positional detector includes a base that is configured to engage and be moved along a curved surface of a welding work piece. At least one position detection apparatus is provided and is connected with the base and configured to measure angular position of the detector relative to a reference vector. In another embodiment, a welding system positional detector includes a weld head and at least one inclinometer mounted on the weld head. The one inclinometer is configured to develop positional data relative to a reference vector and the position of the weld head on a non-planar weldable work piece.

Abstract: A water level includes a hollow metal section having at least one bottom measuring surface and side walls, and at least one position sensor, preferably a bubble level. Usually two bubble levels are provided. The metal section is closed by end caps. A protective cap of an elastic, impact-proof material is placed on the upper side of the metal section and the protective cap is placed on the metal section in such a way that an impact energy introduced at a single point-like location is distributed over a larger surface of the metal section.

Abstract: A tiltmeter device having a pair of orthogonally disposed tilt sensors that are levelable within an inner housing containing the sensors. An outer housing can be rotated to level at least one of the sensor pair while the inner housing can be rotated to level the other sensor of the pair. The sensors are typically rotated up to about plus or minus 100 degrees. The device is effective for measuring tilts in a wide range of angles of inclination of wells and can be employed to level a platform containing a third sensor.

Abstract: An en route package apparatus and methods for operating the same comprise a reservoir having a fluid, a tilt indicator section having an X direction indicator including an X capillary coupled to the fluid in the reservoir, a Y direction indicator including a Y capillary coupled to the fluid in the reservoir, and a Z direction indicator including a Z capillary coupled to the fluid in the reservoir wherein the fluid from the reservoir flows through one of the X capillary, Y capillary, or Z capillary to a respective corresponding direction indicator in response to tilting the en route package sensing apparatus in a direction corresponding to the particular direction indicator.

Abstract: A tilt detecting device for use in various electronic apparatuses such as a watch, electronic notebook or the like. The tilt detecting device includes a projection in a part of a ball containing portion formed in an interior of an insulation case. In the insulation case, two conductive pins are disposed thereon in parallel with each other with a predetermined space, which have a large diameter portion, a small diameter portion and a step between them. In the ball containing portion, a conductive ball is contained therein, which is movable along in a longitudinal direction of the two conductive pins in the ball containing portion when the insulation case is inclined. Only when the insulation case is inclined, the conductive ball is at a position on the large diameter portions to be electrically in contact with the two conductive pins to output a corresponding detection signal.

Abstract: A level formed of a flat card that has a series of register marks that are printed on it. The register marks are designed to fit square on the rectangular card. The primary marks are positioned at the two ends of the card. When looking at the register marks, the user can see any angular displacement between them. This angular displacement indicates an out of level condition. If the marks are viewed as being completely horizontal, the card is level. To use the device, simple stand the card up on the surface to be leveled. The angular displacement of the register marks instantly show whether the surface that the card is resting on is level. In this way, just about anything can be tested for level. The device can also be placed on walls or other objects to draw level lines or reference marks. It is also useful as a template for tracing or drawing straight lines for sewing or other activities.

Abstract: A tilt sensor capable of sensing tilt in two axes includes an outer shell, a magnet at a fixed position inside the shell, and a reference element movable within the shell in response to gravity. Magnetic flux follows a plurality of paths from a pole of the magnet, around the shell, through the reference element, to the opposite pole of the magnet. Magnetic sensors detect changes in reluctance of the flux paths resulting from the movement of the reference element within the shell, from which the angle of tilt can be determined.

Abstract: Leveling instrument—clamping device for mounting leveling instruments to the tripod platform of a tripod. It is provided with a device plate which can be mounted to the bottom of the leveling system and with a stop provided on the upper side of the tripod platform, as well as a clamping device positioned at a distance from the stop with the device plate being mounted removable on the tripod platform via the stop and the clamping device. This allows a quick and secure mounting of leveling instruments by few operations.

Abstract: The invention relates to a device (1) for placing on a person's head (2) to indicate correct or incorrect upright posture during the performance of various activities in a standing or sitting position. The device comprises a balance element consisting of a fixed body (4) which is firmly secured to a headband or similar for attachment to the head (2), and a moveable body (5) which is translationally moveable relative to the fixed body (4), essentially in a plane parallel to or coincident with the main plane of the fixed body (4), whereby the moveable body (5) is designed to move translationally relative to the fixed body (4) when a certain degree of deviation from the correct head position occurs.

Abstract: A level includes a level body and at least one bubble level mounted in the level body. The level body is of a foamed metal. The foamed metal may be foamed aluminum. The level body may be provided with a coating of synthetic material. The level body has recesses for mounting the bubble levels.

Abstract: A ruler for measuring and marking lengths and angles, relative to a horizontal plane by utilizing gravity. The ruler includes a substrate for being oriented relative to a horizontal plane and for measuring and marking lengths, and angle measuring assembly associated with the substrate for measuring and marking angles. The angle measuring assembly has a pointer whose lowermost end is heavier than its uppermost end, which allows the pointer to always remain vertical, regardless what angle the substrate is oriented relative to the horizontal plane, with the tangle the substrate is oriented relative to the horizontal plane being the angle to be measured and being that angular increment of a scale of the angle measuring assembly that the pointer points too.

Abstract: A tilt detecting device for use in various electronic apparatuses such as a watch, electronic notebook or the like. The tilt detecting device includes a projection in a part of a ball containing portion formed in an interior of an insulation case. In the insulation case, two conductive pins are disposed thereon in parallel with each other with a predetermined space, which have a large diameter portion, a small diameter portion and a step between them. In the ball containing portion, a conductive ball is contained therein, which is movable along in a longitudinal direction of the two conductive pins in the ball containing portion when the insulation case is inclined. Only when the insulation case is inclined, the conductive ball is at a position on the large diameter portions to be electrically in contact with the two conductive pins to output a corresponding detection signal.

Abstract: A method using piezoelectric effect is provided for measuring an angle between a reference plane and a plane to be measured. The method can be used to measure the inclination of a plane or for leveling purpose. The method employs an apparatus wherein the main characteristics of the apparatus are simple in structure with no limitation in the measurement range and fewer limitations to the environment. The method may also have the following advantages compact, quick and accurate measurement, easy for multiaxial measurement.

Abstract: A combined leveling device and laser pointer includes a support body which holds a bubble tube and a rotary seat. The rotary seat extends from a front face to a rear face of the support body and has a through-hole which extends from the front face to the rear face and which includes a tapered clamping hole section that is tapered in a direction from the rear face to the front face. The rotary seat is graduated adjacent to the front face, and a clamp is movably provided in the through-hole. The clamp has a plurality of resilient clamp members which are resiliently movable toward or away from one another when the clamp moves into or outward from the tapered clamping hole section. A detachable laser light source unit is insertable into the clamp from the rear face so as to be clamped removably by the resilient clamp members. A hologram is mounted to the rotary seat adjacent to the front face to produce a one-dimensional linear projection image from the laser light source unit.

Abstract: A tool resembling a carpenter's level is used in establishing a precise level line and projecting an existing line using a visible laser beam projector in the same instrument. A manual selector device is provided for switching from a laser beam parallel to a reference surface to one which self-levels in one axis. Methods for switching between modes are described as well as a tilt compensator.

Abstract: An apparatus using piezoelectric effect is provided for measuring an angle between a reference plane and a plane to be measured. Such an apparatus can be used to measure the inclination of a plane or for leveling purpose. The main characteristics of the apparatus are simple in structure, no limitation in the measurement range, and less limitation to the environment. The apparatus also has the following advantages: compact, quick and accurate measurement, easy for multiaxial measurement.

Abstract: A dual usage level marking instrument is provided that includes a leveling rod. This rod has a dotted-type laser device fixed at one end and a straight-type laser device fixed at the other end. Leveling elements are installed on this rod. The dotted-type or straight-type device installed on the both ends emit dotted or vertical/horizontal marking lines. The instrument is used on construction sites for marking measurement.

Abstract: A method and apparatus are described for determining the amount of canting necessary to correct the ski boot-ski interface to compensate for inherent misalignment between a skier's lower leg and the bottom of the sole of his or her boots. The skier's foot is secured in the boot, and the boot is secured on a platform freely rotatable about a longitudinal centerline axis. A rod also freely rotatable about the same axis is centered with respect to the knee by a knee clamp attached to the rod. A pointer affixed to the rod is used to accurately determine the angle between the rod and platform on a scale extending from the boot platform. This angle is then used to guide the placement of shims or the employment of other means to effect the desired orientation of the knee, and consequently the lower leg, relative to the ski, for optimum control.

Abstract: Determination of the verticality of various structures such as high rise buildings and towers is enabled through various methods involving use of a series of tiltmeter devices, a remote positioning system, or a combination of both. These methods are particularly useful in monitoring deviations from vertical during construction work and adjusting a jumpform. The tiltmeters are typically arranged in a line on the structure and polled to characterise varying tilt states in which displacement of each device increases with height up the structure. The remote positioning measurements are typically made in real time using a satellite based system such as GPS. Departures of a survey point on the jumpform from a vertical target line may be used to monitor verticality during the construction process.

Abstract: A susceptor situated within an IC circuit fabrication machine has its level and height calibrated using a levelling apparatus which stands on three legs and includes a plurality of suspended level detectors. The susceptor is positioned between the legs under each one of the level detectors. Before susceptor calibration, the levelling apparatus first is calibrated to a known flat surface. The apparatus then is placed within the fabrication machine and the susceptor is moved to a first position. Distal sensing points of each detector are placed in contact with the susceptor surface. Respective level adjustment mechanisms (e.g., screws) of the fabrication machine then are turned to bring adjust the orientation of the susceptor and bring each level detector to a common level indication. The levelling apparatus includes four level detectors aligned along two axes. Once level, the susceptor is raised until level detectors indicate a common desired process position height.

Abstract: A device and method to measure and correct the cant of a pair of ski boots. A device has a pair of platforms movable with respect to one another. Binding means for the ski shoes are attached to the platform. Each platform is independently rotatable about a longitudinal center line. A pair of vertical indicators indicate the relationship between the respective knee of the skier and the vertical indicators. A second pair of indicators measure the degree of rotation of the respective platforms. Wedges are used to correct the cant and to obtain zero rotation of the respective platforms. The device can also be used to correct the cant of skis with ski boots attached.

Abstract: An adaptable tip sensor is useful for detecting the angular tipping of an object relative to a selected frame of reference. The sensor comprises a case that defines a two dimensional straight sided V-groove in which a disk can roll. A sensing device detects the presence or absence of the disk within the apex of the V-groove. As long as the object does not tip to a predetermined angle, the disk remains in the V-groove apex, and the sensing device produces a first signal. If the object tips to the predetermined angle, the disk rolls out of the V-groove apex, and the sensing device produces a different signal. Fluid in the case damps spurious vibrations. A labyrinth and air bubble in the case enhance desired rolling of the disk when the predetermined tipping has occurred.

Abstract: A magnetometer is integrated with a miniature vibrating beam accelerometer fabricated out of silicon on a common substrate. Dual pendulum-DETF force sensing accelerometers have integrated conductor coils on the pendulums that circulate alternating current to cause an additional pendulum motion also sensed by the DETF transducers for sensing local earth magnetic field. The integrated magnetic and acceleration sensing is used for each of three reference axes in a triaxial inclinometer magnetometer for borehole drill steering and surveying.

Abstract: A spirit level including a body portion having at least one open, hollow end, the body portion having at least one aperture formed on a face thereof, and a clamp insertable into the at least one hollow end, the clamp including at least one vial mounting portion, the clamp being folded and inserted into the at least one hollow end, the at least one vial mounting portion being adapted to be fixedly held in the at least one aperture after insertion of the clamp into the at least one hollow end, wherein a vial is fixedly mountable in the at least one vial mounting portion.

Abstract: A vial for a builder's level includes a body with an interior wall and a body cavity containing a bubble. A marker ring is exposed in the cavity. In the improvement, the ring is embedded in the body and the interior wall and the ring have surfaces machined and coextensive with one another. The bubble moves smoothly across the machined wall and ring surfaces. A new method for making a level vial includes providing an intermediate vial product with a body wall having at least one marker ring embedded in it and machining the wall and the ring to form a wall surface free of discontinuities. The intermediate vial product is also disclosed.

Abstract: A level indicator for a child seat equipped with a rotatable carrying handle rotatably attached thereto, and having a housing in a hub of said pivotal handle with a wall defining an interior region of said hub and an indicator member having an indicator surface. The indicator member is movably received in the interior region and the wall is formed to include a transparent window defined by an edge formed in the wall, the edge being arranged so that the indicator surface is visible through the window when the level indicator is level, with the indicator member moving entirely away from the window edge when the level indicator is not level so that the indicator surface is not visible through the window. The indicator member is disclosed as being a gravity ball that freely rotates in a curved track or a pendulum rotating in the handle.

Abstract: An electro-optical input device for computers or electronic games which uses electro-optical elements to sense input from a user. A user actuation element, such as a directional control pad or a joystick is pivotally disposed on a printed circuit board. Two photoemitters are mounted on the printed circuit board, at or near the circumference of the footprint described by the user actuation element. The photoemitters are positioned 90.degree. apart, one along the North-South axis of flit of the actuation element, and one along the East-West axis. At least one photodetector is mounted to the base at or near the pivot point of the actuation element so that it can receive light from both of the photoemitters. A skirt or flange depends annularly from the actuation element, at or near its periphery, positioned between the photodetector and the photoemitters.

Abstract: A flap holster with the flap pivotally and removably secured to either side of an ambidextrious holster. The holster inlcudes an opening for the insertion and removal of a handgun and a transverse slot below the opening on each side. The flap is pivotally connected to one side of the holster and extends over the handgun opening. On the underside of the flap, an extensible strip is secured at one end to the flap and includes an end hook at the opposite end to engage one of the transverse slots and secure the flap in place. The extensible strap is preferably captured in a fabric tunnel in the underside of the flap. An inextensible flexible strap is secured at both ends to the extensible strap to limit its extension length to avoid over stressing its elastic properties. The hook is preferably a reverse directed tab dimensioned to slip into the transverse slot allowing the elasticity of the extensible strip to hold the flap closed.