Abstract: Polygonal turbine casings which have inherent resistance to deformation by virtue of their many flat sides taking thermal loads etc. in compression or tension, are improved upon by the present invention by way of assembling the casing so as to pre-tension its flats to such an extent that any compressive loads which are felt, never reach a value which would entirely negate the tensile load.

Abstract: Particles contained in the exhaust gas discharged from an internal combustion engine are trapped by a particle-trapping-member disposed in an exhaust gas flow path. The flow rate of the exhaust gas is measured directly or indirectly, and the pressure loss for the trapping member is compared with an exhaust gas flow rate to measure the degree of clogging trapped by the trapping member. When the degree of clogging exceeds the predetermined valve, a command signal for closing an intake throttle is generated to reproduce said particle-trapping-member.

Abstract: A tractor hydraulic control system of the kind comprising a power lift with a hydraulic actuator (12) and a main control valve (17) controlling the supply of fluid from a pump (19) to the actuator, the system including selector valve means (50) interconnected with the main control valve (17) and movable between a first position in which flow to and from the actuator (12) occurs via the selector valve means under the control of the main control valve and the associated system control mechanism (28) and a second position in which the actuator is hydraulically locked in a given position and an external services outlet (51) is placed in communication with the pump. Linkage means (60,61,62) operatively connects the selector valve means (50) and the system control mechanism (28) to condition the main control valve (17) to cause the pump (19) to supply fluid to the external service outlet (51) via the selector valve means on movement of the selector valve means to the second position.

Abstract: A low-pressure casing for a brake booster for automotive vehicles comprising two casing shells. A central ring flange is located at the inner surface of the end wall of each of the two casing shells. The portion of each end wall lying outside the ring flange is of truncated-cone-shaped construction and merges into a cylindrical circumferential casing section. At each of these merger points, a prop ring is inserted to bear against the inner surface of the associated one of the two casing shells.

Abstract: A master cylinder for hydraulically actuated brakes for automotive vehicles includes at least one master cylinder piston with a piston return spring anchored by a central clamping member and a valve body which is slidable relative to the master cylinder piston and which opens a compensating port in the master cylinder piston when the return spring is relieved. The valve body carries an elastic sealing element at its end face close to the compensating port. The outer diameter of the elastic sealing element is greater than the diameter of the compensating port. A pin shaped on the valve body extends through the sealing element and is adapted to plunge into the compensating port on approach of the valve body to the piston end surface which surrounds the compensating port, thus preventing the sealing element from penetrating into the compensating port.

Abstract: Highly saline geothermal brine, such as that produced from the lower geothermal reserve of the Salton Sea geothermal field, is diluted with non-geothermal water of much lower salinity in a mixing zone proximate the high temperature end of a geothermal power plant, and preferably down in the production well just above the production zone, so as to reduce the chloride salt content of the production brine to a level that is at or below the saturated level at reinjection temperatures, thereby preventing any material chloride salt scaling at any location in the plant through reinjection. The permanent cemented-in production casing in the well is protected against the corrosive effects of the hot production brine by means of a removable production liner that is generally coextensive with the casing.

Abstract: Methods by which remote heating circuits are supplied with heat from a thermal power plant by using heat reservoirs located close to the power plant and heating the storage or working medium in a heat exchanger of a heat extraction cycle. The medium is initially heated to a base temperature, for example, when using water, to approximately 95.degree. C., and is further heated immediately prior to being directed into a remote heating circuit to a temperature above 100.degree. C. This two stage heating allows the use of unpressurized heat reservoirs. Additionally, the temperature of the medium is efficiently raised to a level sufficiently to operate the remote heating circuit. Preferably, the medium can further be removed from the reservoirs and heated in a second pass through the heat extraction heat exchanger.

Abstract: The present invention relates to a gas turbine power plant wherein the gas turbine is driven by gases and steam heated indirectly through a heat exchanger by the burning of corrosive fuels. One of the main improvements in the present invention is to utilize a state-of-the-art gas turbine in the power plant.

Abstract: An air-conditioning passive heat recirculating system for heated rooms has a number of heat exchange elements with heat radiation surfaces operating as heat transfer pumps using the Peltier's effect. Said heat exchange elements are arranged at at least one wall or the ceiling of heated room within the flow of the heated air circulating in said room so that their radiation surfaces direct heat from said wall or ceiling area to other parts of the room where the heat is desired and needed.

Abstract: A container is disclosed for storing refrigerated liquids, in particular for liquefied gases, which comprises a steel reinforced concrete outer container and a steel inner container inserted into the outer container, where the steel inner container rests on an insulation and where an annular interspace is present between the outer circumference of the inner steel container and the inner circumference of the outer container. The interspace can be fully or in part of its thickness filled with insulating materials.

Abstract: A radiation heat shield which comprises a plurality of helical grooves distributes possible thermal expansions around its circumference. These potential thermal expansions could be caused by transient conditions or other abnormal operational modes which could reduce the flow of coolant through particular fluid passages of the radiation shield. By incorporating a plurality of helical fluid passages, these potential thermal expansions are distributed around the circumference of the radiation shield and the resulting distortion moments tend to cancel each other and, provided that a sufficient number of turns is possible, eliminate the imbalance.

Abstract: The interior of a tube provided for low temperature operation is shielded from the exterior through a plurality of metal ribbons helically looping around the tube in an intertwined relationship and each carrying a welded on conduit for low temperature liquid whereby one of these conduits serves as a primary or outgoing conductor, and the two others serve as return paths; suitable spacers are provided to position the system in a concentric relation; inner and outermost tubes are preferably corrugated and the immediate interior of the outermost tube is filled with superinsulation.

Abstract: A cryostat which is particularly useful for containing superconducting windings for a magnet to provide high strength magnetic fields for NMR imaging comprises a set of nested annular vessels in a suspension system which permits transport of the cryostat and magnet assembly with vacuum conditions intact. In particular, sets of transverse ties linking certain vessels to the next adjacent outer vessel are employed to prevent transverse motion of the cryostat assembly. Furthermore, during transport, a system of pins is employed to prevent axial motion, while at the same time minimizing thermal conductivity. During transport, the inner annular assemblies are locked in a fixed axial position which permits transport of the cryostat in a vertical position.

Abstract: A method and apparatus for controlling the operation of an add-on heat pump water heater unit is disclosed. A combination of a thermally conductive tube having a flattened portion and a thermostat mounted thereto is utilized to sense the temperature level of water in a tank to which the heater unit is connected. The tube and thermostat are additionally insulated from the ambient. A circulating pump is provided and connected to the water thermostat such that the pump is energized only when it is necessary to operate the heat energy adding unit.

Abstract: A combination refrigeration circuit and hot water preheater is disclosed. Specific temperature sensing arrangements in combination with a bypass circuit and a continually operating pump are disclosed to obtain effective control of the hot water preheating system in combination with a refrigeration circuit. Additionally disclosed is an air conditioning system having a combination desuperheater hot water preheater built into a compressor section thereof to eliminate field connections to a hot water preheater.

Abstract: A heat exchanger system includes a boiler and a double sleeve pipe which is disposed in the boiler and has coaxial inner and outer pipes. The inner pipe is connected to a heat pump, and carries a first fluid medium. The outer pipe is connected to a fluid circuit which includes a pump and a three-way valve. The three-way valve can selectively connect into the fluid circuit a further three-way valve and a heating system, and the further three-way valve can selectively connect a further boiler into the fluid circuit. The inner surface of the inner pipe is preferably ribbed, and there is preferably at least one longitudinally extending wall in the inner pipe which divides it into two or more separate channels.

Abstract: A single-body type air conditioner in which a casing and a base plate held in the casing are defined by an intermediate partition to form a room side section and an outdoor side section; a heat exchanger and a fan are placed in each of the sections; a driving motor is positioned to drive the fans; an air blowing passage is formed below the room side heat exchanger and an air intake grille is formed at the upper part and an air blowing louver is formed at the lower part of a front panel. Air blowing in the vertical and lateral direction is attainable as desired.

Abstract: A flow stopping plug is formed in a conduit such as a fluid transmission pipeline by tapping a relatively small hole in the side of the pipe directly adjacent the desired location of the plug and inserting a flexible bag through the hole using a radially extendable bag insertion apparatus having a tube containing the bag initially in a collapsed or folded condition. The bag is connected to a conduit assembly which provides for filling the bag with water in the deployed position inside the pipe. After the bag is filled with water, a freezing process is carried out preferably using a cryogenic fluid which is circulated around the exterior of the pipe section directly adjacent to the bag. The conduit assembly connected to the bag may be placed in communication with a source of heating fluid for melting the ice plug formed within the bag after completion of the work process in connection with which the ice plug was deployed.

Abstract: The invention concerns the production of deformable hollow reinforcements of revolution by a three-dimensional weaving. In a network of rods 18 held and rotated about a vertical axis 11 by rotary perforated plates 52, 53, 54, there are inserted in oblique crossed directions, i.e. non-radial directions, threads in the form of chain stitch loops produced by a knitting device 32. The chain stitches are downwardly compacted by the lower edge of the plate 52 which is inclined for this purpose.

Abstract: In a circular knitting machine for hosiery articles, a plurality of generally banana-shaped sinker-pressing cams are mounted beneath a lid or cap to float radially between an inner ring cam and a plurality of miniature pneumatic rams and attendant plungers, which are arranged in a circular path around the outsides of the sinker-pressing cams. Each of the rams has its plunger engaged with the outer peripheral surface of one of the sinker-pressing cams, and is connected to a pneumatic control means, which is operable selectively to force the ram plunger against the associated sinker pressing cam to urge it radially inward against the outer ends of the sinkers. With this construction the sinker-pressing cams can be selectively utilized depending upon the type of article being produced on the machine.

Abstract: A coupling strip for a slide fastener, which can be utilized as part of a stringer half together with a fabric tape of which it forms a part, or alone as a stringer half, is produced by crocheting at least two rows of knots using bearded (spring-type) or latch needles and respective yarn guides on a crocheting machine, a continuous coupling element in coil or meander form and composed of a synthetic resin monofilament being inserted as a weft across these rows.

Abstract: The run-resistant toe portion is of substantially the same dyed shade and has the same sheer appearance as the adjacent foot portion of the hosiery article. The run-resistant toe portion is knit with every other course being knit of a yarn which is capable of being dyed and the remaining courses are knit of a dye-resistant yarn which is not capable of being dyed. Intervening single courses of the toe portion are knit with alternating tuck and plain stitch loops in adjacent wales while alternating courses are knit with plain stitch loops in every wale and of a smaller stitch loop size to enhance the run-resistant characteristics of the toe portion.

Abstract: A key for a lock of the plunger operated type in which an elongated housing has an internal axially movable plunger which releases locking elements when moved toward the open end of the housing, said key having a body with elongated fingers forwardly from the housing and an elongated mandrel disposed between the fingers. A spacer is disposed at the rear end of the fingers and protrudes forwardly from the foremost face of the key housing for abutting a portion of the lock to limit the distance the fingers can extend into the lock. The housing has a head portion which is axially adjustable in relation to the spacer to vary the amount the spacer projects forwardly from the housing.In one embodiment of the invention internal structure is provided that allows the fingers to shift forwardly a predetermined distance if the forward end of the housing is removed by grinding in an effort to modify the key for use in locks with which it is not intended for use.

Abstract: A lock cylinder attaching device is of the type for use in a vehicle movable closure lock and comprises a support for attaching an inner end of a lock cylinder to a vehicle body member in addition to means for attaching the outer end of the lock cylinder to the vehicle body member.

Abstract: A separating and feeding system for a shot peening machine is of the type which includes blast wheels mounted on a housing of the machine and capable of propelling a plurality of shot generally downwardly into a critical blast region within the housing for shot peening a plurality of springs passing therethrough. The springs are supported on and separately conveyed along a pair of spaced spinner rolls along a peening path into one side of and through the critical blast region. The separating and feeding system includes an entrance chamber within the housing adjacent the one side of the critical blast region. An elongated horizontally extending chain is mounted relative to the housing for continuous movement from a first end exterior of the housing through an opening in a wall of the housing to a second end within the entrance chamber at the one side of the critical blast region.

Abstract: An improved apparatus for manufacturing a rupture disk containing one or more scores or perforations from a sheet metal section comprising the steps of cutting the sheet metal section into a disk, forming a concave-convex dome in the disk by applying pressurized fluid to one side thereof, and then forming one or more scores or perforations in the concave-convex dome of the disk while continuing to apply pressurized fluid thereto.

Abstract: A method and an apparatus for the explosive shaping of metal tubing are provided. A die including a pair of die halves are opened and closed by means of a clamping assembly attached thereto. The die halves include a plurality of die segments which are coupled in series. A breech is secured to one end of the die. A shotgun shell may be loaded into the breech and fired by means of a detonator. The necessary force for deforming the tubing is accordingly provided. A water retaining block is secured to the end of the die opposite the breech so that water can be held in the tubing prior to detonation of the shell.

Abstract: A tightening device for the gripping jaws of a plate stretcher comprises one push rod for each pair of gripping jaws sliding in guides in the gripping head in the stretching plane, and having hinged thereto two link rods which are also hinged to the gripping jaws, the gripping jaw moving synchronously rearwards for the closing operation and forwards for the opening operation, in two guides disposed in V-formation to each other. The link rods are coupled to the gripping jaws in a disengageable manner to avoid damage to the link rods and tightening device if tearing of the plate takes place during the stretching operation, or on account of any difference in the gripping of the plate by the upper and lower gripping jaw causing generation of very large but different forces on the two link rods. The link rods are in the form of angle levers each having a long and short arm pivotally connected to the hydraulically mobile push rod.

Abstract: The jack comprises a fixed jaw, rigidly associated with the jack body, and a movable jaw facing said fixed jaw and being connected to a piston sealingly movable inside a cylindrical chamber. In the body, first and second chambers are provided, respectively in communication, through a first delivery conduit and first intake conduit, and through a second delivery conduit and second intake conduit, with the cylindrical chamber and a working fluid reservoir, in the first chamber there being sealingly movable a high pressure piston, whereto is connected a lug passed through the second chamber in sealed relationship therewith, wherein it acts by contact on an elastically biased low pressure piston, the high pressure piston being connected at the free end thereof to an actuating lever handle.

Abstract: There is disclosed herein an acoustic or ultrasonic power meter which includes a liquid crystal cell for detecting acoustic energy and a control circuit for applying an electric field to said cell. The liquid crystal cell includes a liquid crystal material having elongated molecules. The preferred liquid crystal is in the form of a layer of the nematic type which is homeotropically aligned. The elongated liquid crystal molecules exhibit positive dielectric anisotropy wherein the dielectric constant parallel to the molecule's axis is greater than the dielectric constant perpendicular to the molecule's axis. In the unexcited condition, the nematic layer is dark. In the ultrasonically excited condition, the nematic layer exhibits birefringence. A restoring electric force can be applied to the liquid crystal material to suppress the acoustically-induced birefringence condition of the cell to the dark appearance associated with the unexcited condition.

Abstract: A method is disclosed for the recognition of irregular combustion processes in an internal combustion engine. In this method, a parameter characterizing the course of combustion--for example, pressure, light in the combustion chamber, sound and the like--is detected by means of a sensor, and the sensor signal is integrated within a predetermined crankshaft angle range or time interval of the combustion cycle and compared with a signal integral obtained in a previous cycle. The signal integrals of cycles directly following one another are compared, and monitoring is performed as to whether a signal increase above a predetermined threshold is occurring, in the case where combustion has heretofore been regular, or the signal is decreasing by more than a predetermined amount, in the case where irregular combustion has been taking place. In the first case, the result is the recognition of irregular combustion; in the second case, the result is the recognition of the end of the irregular combustion.

Abstract: A knocking detection apparatus for multi-cylinder engines, capable of detecting knocking through sensing pressure pulsation propagating through the cooling water flowing in a cylinder block surrounding the cylinders. The knocking detection apparatus has a diaphragm facing the space downstream from the detection apparatus as viewed in the direction of flow of the cooling water, and a transducer dixed to the diaphragm.

Abstract: A noble gas leak detector is provided using a non-evaporable getter pump to remove active gases but not noble gases during leak detection. The vacuum system is constructed of all-metal valves, metal connection devices and metal passageways to reduce out gassing and minimize the permeation of helium into the system. Valves are appropriately located to seal off unnecessary devices during the actual leak detection. In addition, a process of calibrating a noble gas leak detector is provided using americium 241 alpha as the calibrating source.

Abstract: A free falling or projectable penetrometer for simultaneously determining a multiplicity of ground characteristics during penetration and retracking cycles and while at rest following full penetration. The apparatus employs a multitude of sensing elements and is further characterized by the presence of at least three electrode pairs one aligned with the central axis of the penetrometer with the other two pairs being positioned orthogonally in a common plane that is itself perpendicular to the central axis. An onboard power supply is included together with telemetry equipment to generate ground characteristics and transmit such signals.

Abstract: The optimum shift position indicating device of a vehicle comprising: a vehicle speed sensor for detecting a running speed of the vehicle; an engine rotation sensor for detecting a rotational speed of an engine; an engine load sensor for detecting an engine load; an operational circuit in which a driving power at present is calculated from an engine torque obtainable from the engine rotational speed and the engine load, subsequently, required engine torques at respective shift positions are calculated from the driving power, further, fuel consumption rates at the respective shift positions are obtained from the engine rotational speeds and the required engine torques at the respective shift positions, and information on the optimum shift position where the best fuel consumption rate is obtainable is outputted; and shift position indicating elements for indicating an output from said operational circuit; and capable of giving a driver the information on the optimum shift position where the best fuel consumptio

Abstract: An economical compact heat exchanger cleaning and testing device and a method of cleaning and testing heat exchangers using said device is disclosed. The device involves a T-shaped fitting, one end of the top portion of the "T" being adapted to be connected to a source of water under pressure and the other end being adapted to be connected to the hose leading to the heat exchanger. The other leg of the "T" is adapted to be connected to a source of air pressure and contains both an air pressure gauge and a modulating valve. By introducing water under pressure and alternately increasing and decreasing the air pressure, a shock wave is produced which tends to remove any accumulated scale in the heat exchanger. After the heat exchanger has been completely cleaned the heat exchanger can be filled with water under pressure and the air pressure can be increased up to a measured pressure to determine whether or not there are any leaks in the system.

Abstract: An apparatus for detecting combustion timing in an internal combustion engine comprises: a microwave unit including a microwave oscillator for generating a microwave having a predetermined frequency, a transmission and reception separator for separating transmitted and received microwaves from each other, and a detector for detecting the received microwave so as to be converted to a low frequency signal; a probe including a microwave sensor for radiating the microwave from the separator into a combustion chamber and receiving a reflected wave, and a light sensor for electrically detecting light emitted upon combustion in the combustion chamber; and a processing unit including a peak detector circuit for detecting peaks of a microwave signal supplied by the detector, a luminous signal processor for detecting a peak value of a luminous signal supplied by the light sensor in each cycle and also detecting the time when the luminous signal reaches an intensity having a predetermined proportion to the peak value th

Abstract: A method and apparatus for determining the extent of defects in ferromagnetic tubular elements comprising a continuous string for use in an oil or gas well is disclosed. The tubing trip tool measures tubing average wall thickness, local defects, such as corrosion pitting, and axial defects, such as sucker rod wear during removal of the tubing from the well. Tubing velocity is also measured, and couplings between tubing sections are detected and counted, in order to specify the axial location of defects on each tube, and also provide a profile of the condition of the overall string. A saturating magnetic field and a fluctuating magnetic field are applied to the tubing and the magnitude of the induced fields and the changes are measured to quantify defects in the tubing.

Abstract: Apparatus for the optical observation of the evolution of instabilities between two fluids having different densities subject to high initial pressures, of the type comprising an observation chamber with parallel faces containing the two fluids, initially separated by a diaphragm, and wherein it comprises in combination the arrangement of the observation chamber within a tight enclosure equipped with static pressurizing means and whereof one face is constituted by an optical observation window parallel to the two parallel faces of the observation chamber, the diaphragm having a straight cylindrical shape and is coupled to a mechanical extraction shaft, the geometrical axes of the diaphragm and the extraction shaft being perpendicular to the faces of the observation chamber, the extraction shaft sealingly sliding through the wall of the enclosure opposite to the said window, while part of the extraction shaft external of the pressure enclosure is integral respectively with a piston sliding within a cylinder an

Abstract: An ultrasonic transmitting element and an ultrasonic receiving element are arranged in a sample liquid in opposition to each other. Either the ultrasonic transmitting element or the ultrasonic receiving element is finely vibrated, and the difference between the velocities of sound in the sample liquid and another sample in the sample liquid is displayed on a CRT.

Abstract: Plate stock of uneven and variable thickness is tested for defects by means of ultrasonics whereby the zone adjacent the front surface and up to a depth of the minimum plate thickness is detected conventionally, but under utilization of a novel method the zone of variable thickness adjacent the rear wall is tested by detecting any echo in a gating period (15) that is returned from that zone or from the rear wall, and such an echo is used to set up a supplemental gating period during which either none or the rear wall echo will occur and in the latter case the setting up of the supplemental gating period is interpreted as having resulted from the presence of a defect (for example, echo 12) so that the occurrence of the rear wall echo 9 within the supplemental gating period is registered as an indication of a defect.

Abstract: An ultrasound imaging system is provided having an articulated arm for holding a transducer. Signals representative of the angular position of the arm joints are scaled up to a voltage range over which the restricted range of movement of each joint is distributed. The scaled signals are combined to produce a plurality of combined angular signals, which then may be digitized and used to compute the X-Y position of the transducer.

Abstract: A transducer assembly is provided which performs simultaneous imaging and flow measurement. Separate imaging and Doppler transducers are mounted on one face of the assembly. Each transducer type is backed by backing material which provides damping in accordance with the performance criteria of the different transducer types. The transducer types may be mechanically focused in the same direction so that flow measurements are made in the center of the area being imaged.

Abstract: An article and method is provided for remotely optically measuring high transient isotropic pressures. The arrangement employs a fluorescent crystal (such as a ruby) secured to one end of an elongate optical fiber waveguide for placement in the vicinity of a high pressure occurrence such as near an explosion. Light launched into the free end of the waveguide travels the length thereof to stimulate the crystal, which in the case of a ruby, fluoresces in the red, the wave length of which varies in response to isotropic pressure on the ruby. This red light output is transported back along the same optical fiber waveguide to the free end where its wavelength change is monitored and translated into a pressure value on the crystal.

Abstract: A circuit having a transducer which normally provides a non-linear output as a function of a stimulus to which the transducer is responsive. The circuit is provided with a feedback resistor from at least one of a pair of output terminals coupled to the transducer, and the feedback resistor is coupled to the power input of the transducer. Any change in the output voltage will cause a current change through the transducer, and this current change has a linearizing effect on the output voltage. The circuit is especially adapted for use with a Wheatstone bridge having a power amplifier coupled to the input thereof and a differential amplifier coupled to the output thereof. In such a case, a pair of feedback resistors couple the output terminals of the differential amplifier with the input terminals of the power amplifier.

Abstract: A thermal conductivity vacuum gage has a vacuum-sensing probe and a separate operating unit for indicating the vacuum sensed by the probe and supplying electrical power for the vacuum sensing by the probe. An electrically-conducting cable connects the probe to the operating unit to form measuring and power supply circuits therebetween. The portion of the measuring circuit and the portion of the power supply circuit in the operating unit are identical or common, i.e. the same circuit portion, so that variations in the operation of this common circuit portion affect circuits the same in contrast to prior gages having separate measuring and power supply circuits, whereby variations in the operation of one could affect the other.

Abstract: A sampling system for stool analysis provides an elongated handle and a cylindrical coring device, said handle including means for releasibly holding said coring device. The coring device is inserted into the stool to collect a representative sample. The sample is removed for analysis, as required.

Abstract: In a push-button tuner including a tuning slide member which has a positioning portion in one side edge and which is slidable in a predetermined direction, a lock member which is movable in a direction orthogonal to the sliding direction of the tuning slide member and which is provided with cam member grasping means, and a cam member which is turnably supported by the lock member. The cam member comes into engagement with the positioning portion of the tuning slide member and has its position in its turning direction fixed by the cam member grasping means. The positioning portion of the tuning slide member is provided with an elastic piece. When the lock member has been thrust to the tuning slide member, the cam member comes into pressed contact with the elastic piece, and the elastic piece retreats. Thus, the abutting force between the tuning slide member and the cam member is lightened.

Abstract: In a heavy-duty pump jack as used in oil well pumping, a leverage beam is oscillated by a motor-driven crank and the leverage beam acts upon the walking beam through an adjustable stroke controller.

Abstract: A motor-compressor unit comprising a shell, a compressor, and a motor. The compressor includes a yoke and a slide block to transmit motion from a compressor crankshaft to a plurality of compressor pistons. The yoke includes left and right longitudinally extending side wall portions, and upper and lower front and rear connecting portions secured to and transversely extending between the left and right side wall portions. The upper and lower front connecting portions define a front transverse opening, and the upper and lower rear connecting portions define a rear transverse opening. The slide block is supported by the yoke for longitudinal sliding movement through the front and rear transverse openings.