Abstract: A screw having stacked screw heads includes a screw shank portion with a thread and a screw head portion rigidly connected to each other. The screw head portion is driven to bring the screw shank portion to rotate. The screw head portion includes a first screw head and a second screw head. The first screw head has a first shaped groove on its top plane to receive an operating torque. A neck portion is connected to a bottom plane of the first screw head and a top plane of the second screw head. The second screw head has a second shaped groove on its top plane. The neck portion or the connection between the neck portion and the first screw head or the second screw head has lower torsional endurance than each of the first screw head and the second screw head.

Abstract: The present invention relates to a screw drive having integrated torque protection, wherein two screw drives are incorporated in a screw head, one drive being an internal polygonal drive and the second drive being an internal multilobular drive. In addition, the invention relates to a screw having a screw drive.

Abstract: A polyaxial screwdriver for inserting a bone screw in a vertebra. A polyaxial bone screw assembly includes a coupling element. When a screw engaging end of the polyaxial screwdriver is lowered on the head of the bone screw, the complimentary surfaces of the screw engaging end of the screwdriver and the head of the screw self-align. A ratchet mechanism formed in the screwdriver provides progressive and automatic locking of the polyaxial screwdriver to the coupling element and prevents the accidental unthreading from the coupling element. In another embodiment of the polyaxial screwdriver, a collet slides over the outside surface of the upper end of the coupling element and locks on to the coupling element. In yet another embodiment of a polyaxial screwdriver, the outer sleeve of the polyaxial screwdriver has a split end that securely engages the coupling element.

Abstract: A drive system with full surface drive contact. The drive system tends to maximize the surface contact pattern or area at typical bit-recess reaction (drive) torque values, thereby tending to minimize bit-recess surface contact stresses, coating damage, recess ream and premature bit fatigue failure. The drive system comprises a fastener and/or bit having drive surfaces formed of either polygon involutes or a single arc construction. A punch is also provided for forming a recess in either the fastener or the bit, wherein the punch has corresponding surfaces.

Abstract: A security fastener for installation on a wheel having a recess hole extending from a recess entrance of a first diameter comprising an end portion concentric with a longitudinal axis of the fastener, the end portion configured to mate with a corresponding element of the recess hole, an intermediate skirt portion having a side wall region with a diameter within about 6 millimeters of the diameter of the recess entrance, a drive portion having a tapered outer surface and a plurality of circumferentially spaced longitudinally extending key-receiving grooves in the tapered outer surface arranged in a lock pattern to which a driving torque may be applied, the tapered outer surface sloping downward and outward away from the longitudinal axis of the fastener from a top surface to the skirt portion at a taper angle of at least 11 degrees.

Abstract: A fastener including a sleeve having an elongated portion, a head with a bearing surface, and an internal threaded portion, a core bolt disposed within the sleeve and having a head and a shank portion having an external threaded portion engageable threadedly with the threaded portion of the sleeve. An insert is disposed within the sleeve and surrounds a portion of the core bolt. A seal element is attached to the sleeve and juxtaposed with the bearing surface of the head of the sleeve. The fastener is adapted to be installed in a structure. The electrical contact of the fastener reduces the potential difference between it and the structure, which provides a direct path for continuous propagation of electromagnetic waves, reducing electromagnetic wave scattering and minimizing the electromagnetic signature.

Abstract: A threaded fastener includes a head end, a shank and an entry end, the head end located at one end of the shank and the entry end located at an opposite end of the shank. The head end includes an end face with a drive recess configured for being driven by multiple drive bit shapes, including a star or six lobe drive, a Phillips drive, a square drive and a flat blade drive.

Abstract: A dental implant for insertion in the jaw bone of a patient is provided. The dental implant has an elongated body having a longitudinal axis and a coronal end, an interior bore extending longitudinally from the coronal end, and a plurality of longitudinally extending anti-rotation structures formed at the inner circumference of the interior bore. The anti-rotation structures have a first set of anti-rotation structures constituting a first anti-rotation feature and a second set of anti-rotation structures constituting a second anti-rotation feature which is independent from the first anti-rotation feature. The anti-rotation structures of the first set and the anti-rotation structures of the second set extend in part over a common length along the longitudinal axis.

Abstract: A screw element includes a screw axis, a shank for inserting in a bone, and a drive portion for engaging a screw driver. The drive portion includes a first wall defining a first recess and a second wall defining a second recess. Drive grooves are formed in the first wall and extend parallel to the screw axis. The second wall extends axially from a free end portion of the screw element to the first wall and has an inner diameter that continuously increases from the first wall towards the free end portion. A plurality of guide grooves are formed in the second wall at circumferential positions corresponding respectively to circumferential positions of the drive grooves. The guide grooves extend further radially from the screw axis than the drive grooves and guide the screw driver from the free end portion of the screw element to the drive grooves.

Abstract: A screw element includes a screw axis, a shank for inserting in a bone, and a drive portion for engaging a screw driver. The drive portion includes a first wall defining a first recess and a second wall defining a second recess. Drive grooves are formed in the first wall and extend parallel to the screw axis. The second wall extends axially from a free end portion of the screw element to the first wall and has an inner diameter that continuously increases from the first wall towards the free end portion. A plurality of guide grooves are formed in the second wall at circumferential positions corresponding respectively to circumferential positions of the drive grooves. The guide grooves extend further radially from the screw axis than the drive grooves and guide the screw driver from the free end portion of the screw element to the drive grooves.

Abstract: The combination of a driver and fastener that allows a user to insert and remove the fastener by applying larger than normal torque loads to it includes: (a) a fastener with a proximal end handle and a distal end head configured to provide a standard indentation and an additional recess that provides additional surface area that allows larger torque loads to be applied to the fastener, (b) a main driver with a shaft having a central bore, a handle at its proximal end and a head at its distal end configured to allow it to be temporarily inserted into the fastener's head, and (c) an awl driver having an awl shaft with an awl handle affixed to its distal end and its proximal end including a tip configured to allow it to pass through the main driver's bore and be brought into contact with the fastener's head where it is used to cut into the fastener cannula so as to temporarily adhere the awl driver to the fastener.

Abstract: An adjusting screw configured to be adjustable by multiple different tools is described. An example adjusting screw includes a cylindrical body portion having a first end, a second end, and an outer curved surface. The example adjusting screw also includes a first raised portion on the first end and offset from a longitudinal axis of the cylindrical body and a second raised portion on the first end and offset from the longitudinal axis of the cylindrical body and opposing the first raised portion. Each of the first and second raised portions is configured to engage a first socket to turn the cylindrical body about the longitudinal axis. Additionally, the first and second raised portions are configured to engage a second socket larger than the first socket to turn the cylindrical body about the longitudinal axis.

Abstract: An assembly improving, lower mass fastener head that is easier to handle and reduces the amount of material that is required in manufacturing the fastener comprises three lugs at multiples of 60 degrees around an axis of a threaded body. Those portions of a hex head that are not necessary for application and transmission of torque, nor necessary to resist axial loading, nor necessary to axially stabilize the fastener head within current driving tooling may be removed. Compatibility with existing hex head tools is maintained while improving handling of the fastener by an assembler and reducing material used in the fastener head.

Abstract: A milling tool includes a toolholder having an insert-receiving pocket, a cutting insert having a hole provided therein, the cutting insert being disposed in the pocket and a clamping screw having a male key grip at a first end and zero or more key grips at a second end. The clamping screw extends through the hole in the cutting insert into a threaded hole in the toolholder so that threads on the clamping screw mate with threads in the threaded hole. The male key grip is remote from the cutting insert. The second end of the clamping screw includes an enlarged head including a clamping surface that abuts a clamping surface in the hole of the cutting insert. A clamping screw suitable for a milling tool is also provided.

Abstract: According to example configurations, a modified screw head includes one or more slots or grooved channels. A screwdriver device includes a tip that can be inserted into a cavity in the head of the screw to torque the modified screw into an object. The screwdriver device includes a sleeve. The sleeve slides along a shaft of the screwdriver. The sleeve includes inward protruding posts (e.g., pins, fingers, etc.). Sliding of the sleeve over the screw's head requires that inward protruding posts in the sleeve be aligned with the grooves on the sidewall of the screw's head. Subsequent to aligning and sliding the sleeve into the grooved channels of the screw's head, the user twists the sleeve to secure the screw head to the screwdriver's tip. The sleeve can be spring-loaded to pull the head of the screw toward a handle end of the screwdriver after a user releases the sleeve.

Abstract: Various embodiments described herein provide a fastener system having straight walled driving surfaces that provides a reliable stick fit feature, while also improving stability of engagement between the system components. A feature of the new system is to allow engagement of existing standard straight walled drivers in the new system.

Abstract: According to example configurations, a modified screw head includes one or more slots or grooved channels. A screwdriver device includes a tip that can be inserted into a cavity in the head of the screw to torque the modified screw into an object. The screwdriver device includes a sleeve. The sleeve slides along a shaft of the screwdriver. The sleeve includes inward protruding posts (e.g., pins, fingers, etc.). Sliding of the sleeve over the screw's head requires that inward protruding posts in the sleeve be aligned with the grooves on the sidewall of the screw's head. Subsequent to aligning and sliding the sleeve into the grooved channels of the screw's head, the user twists the sleeve to secure the screw head to the screwdriver's tip. The sleeve can be spring-loaded to pull the head of the screw toward a handle end of the screwdriver after a user releases the sleeve.

Abstract: A metallic head of a fastener includes merlon portions between crenel portions. The crenel portions form a slot which may be used to tighten or loosen the fastener. An insulating material covers portions of the metallic head to prevent human contact with the metallic head and terminal lugs secured thereby. The metallic head defines a counter bore portion. Inner walls of the counter bore portion may be formed into a hexagon. The insulating material may extend into the counter bore portion covering the inner walls, as well as the surfaces of the crenel portions. The bottom of the counter bore may remain uncovered to facilitate signal testing with a test probe.

Abstract: The present invention provides a fixation device that includes an elongate shank defining a longitudinal axis and having at least one engaging member for applying the fixation device within tissue and securing the fixation device in the tissue once implanted formed thereon, and a drive head having a proximal end, a distal end and a radial cross-sectional geometry, where the drive head is mated to the elongate shank, and includes at least one anti-rotational member integral therewith. Fixation device kits utilizing the fixation device, and methods of fixation in tissue are also provided.

Abstract: Interference surfaces are constructed on inner transition surfaces between wings of a fastener having a spiral recess. A portion of the transition surface is tapered to provide the interference. A standard driver for a spiral recess will engage the interference surface to create a “stick fit” engagement. The punch is formed using a wire EDM operation to construct tapered surfaces within the die cavity of a hob. The hob is machined down to obtain the desired depth, which is measured up from a gage spot indicative of the sticking point.

Abstract: A recessed head screw includes a head portion having a driver-engaging part between top and bottom faces thereof. The driver-engaging part includes a recess extending downwardly from the top face, four spaced-apart slanting walls slanting downwardly and convergingly from the top face, and four first bearing pieces each spacing two adjacent ones of the slanting walls and each having a four-sided first bearing face, and two substantially triangular second faces interconnected by the first bearing face. At least two second bearing pieces extend downwardly and respectively from bottoms of two opposite first bearing pieces. Each second bearing piece has a connecting face, and a third bearing face extending downwardly and inwardly from the connecting face. The connecting face inclines with respect to both of the third bearing face and the respective first bearing face.

Abstract: The fastening metal fitting which allows satisfactory fastening by a hexalobular wrench at the time of assembly and allows loosing or fastening not only by a hexalobular wrench but also by a wide use of wrenches such as a common hexagon wrench at the time of disassembly and repair, which includes the head and the axial portion having the screw portion, in which at the center of the head, the tool insertion hole is formed with the hexagonal socket portion and the circularly-arced notched portions outwardly protruding from the respective corners of the socket portion which are provided at the corners continuously.

Abstract: A fastener has a recessed drive configuration with outlet channels extending from the recessed drive configuration to the outer surface of the fastener.

Abstract: A locking cap is selectively locked into place within a tubular opening, such as the open end of a standpipe used to charge a building sprinkler system. The locking cap has an expandable sleeve and a spreader member. As a key is turned, the spreader member is drawn into the expandable sleeve which is urged outward. The outward movement of the expandable sleeve increases a frictional component such that the expandable sleeve becomes frictionally locked within the tubular opening. The key has an end design that is complemented by an end of an actuator shaft such that the likelihood of unauthorized removal of the locking cap is reduced.

Abstract: A screw (10) and driver (30) system comprises a range of screws and a driver. Each screw has a head (12) having a driving recess (14) in its surface (13) for engagement by the driver. Each screw has a longitudinal axis (100). The recess (14) of larger screws in the range have a plurality of superimposed recess-tiers (16a,b,c) of decreasing size with increasing depth from said surface. Each recess-tier has substantially parallel driving surfaces. They are substantially parallel the longitudinal axis. The driver and recess are shaped so that, when the driver is engaged with the recess of any screw in the range, torque applied to the driver is transmitted to the screw through said driving surfaces. At least one recess-tier (16c) of at least smaller screws in the range has a rib (20) which is parallel the longitudinal axis (100) and encroaches into the space of the recess-tier occupied by the driver when it is engaged with the recess.

Abstract: A fixed pillar with heat loss is a fixed pillar for losing heat. The fixed pillar with heat loss includes a metal body, a screw thread and a plurality of grooves. The metal body is a hollow body. The plurality of grooves is respectively set on two sides of the metal body and communicating with each other. The screw thread is set on one end of the metal body to fix a circuit or other electric devices. Air flows into one side of the metal body and then passes through the inner part of the metal body and last flow out from another side of the metal body. Accordingly, the metal body exchanges heat with the air to lose the thermal energy quickly.

Abstract: A threaded fastener capable of being reduced in size and weight. A pair of side wall surfaces of each of six radially outwardly projecting, torque transmitting portions lie on straight lines passing through the center line in a cross section perpendicular to the center line so as to transmit torque through the side wall surface, whereby the direction of a surface orthogonal force N applied to a force-applied point P by a wrenching tool coincides with the direction of an effective wrenching force F. This arrangement reduces an operation force required for rotating the wrenching tool and accordingly the load acting on each of the torque transmitting portions, in comparison with a conventional hexagonal head. That is, it is possible to reduce the diameter of the head portion of the threaded fastener and the size and weight of the head portion, while avoiding deformation of the side wall surfaces through which the torque is transmitted.

Abstract: Disclosed is a stopping point comprising a connecting eye (1) used with stopping or lashing means. Said connecting eye is rotatably mounted on an anchoring screw (4) which is undetachably connected to a supporting disc (10). The base (2) of the connecting eye leans against a ring flange (13) of the anchoring screw (4) head (5) via a first series of rolling bodies (11) and against the supporting disc (10) via a second series of rolling bodies (12) so as to ensure high rotatability of the connecting eye (1) in relation to the anchoring screw (4).

Abstract: A screw and driver system includes a range of screws and a driver. Each screw has a head having a driving recess in its surface for engagement by the driver. The recess of larger screws in the range have a plurality of superimposed recess tiers of decreasing size with increasing depth from said surface. Each tier has substantially parallel driving surfaces and torque applied to the driver is transmitted to the screw through the driving surfaces. At least one tier of at least smaller screws in the range has a rib. Engagement of the driver with the recess causes deformation of rib, and hence creation of an interference fit of the driver in the recess.

Abstract: A socket capable of adapting itself to an open end of one of a plurality of wrenches of different sizes is disclosed. The socket comprises a lower connecting section including a cavity, and a four-sided actuation block projected from a top of the connecting section, the actuation block including two curved bearing surfaces having different curvatures. The actuation block is operable to be held by an open end of the wrench with two opposite interior surfaces of the open end of the wrench being in contact with two points of the bearing surfaces so that turning the wrench will fasten or unfasten an object coupled to the cavity.

Abstract: A fastener is described having a head formed with a recess which accommodates a square head driver, symmetrical drivers, such as PHILLIPS™ style drivers, asymmetrical style cross head drivers, such as POZIDRIV® style drivers, and combination square and cross drivers without compromising performance of the drivers.

Abstract: A mine roof bolt for use with a cable comprises a barrel having a first end and a second end, the second end having a rounded surface, a bore extending through the barrel between the first end and the second end and including a tapered portion, the bore sized to receive the cable, a pair of wedges sized for placement in the tapered portion of the bore and adapted to frictionally engage a cable disposed in the tapered portion of the bore, a recess defined in the first end of the barrel, and a driving nut sized for insertion in the recess and adapted for engagement by a driving tool.

Abstract: A captive nut assembly that allows removal of one or more workpieces and/or provides access to an area between a plurality of workpieces is provided. The captive nut assembly includes a screw with an elongated shank that is adapted to be located in an opening of one or more workpieces and terminates at one end in an enlarged head. The shank has a threaded portion adapted to be secured to an other workpiece. The captive nut assembly also includes a captive nut that is rotatably mounted on the threaded portion of the screw and moveable along the shank of the screw with the head of the screw being located within the bore of the captive nut.

Abstract: A boring tool is proposed which has a cutting portion at one end thereof, a driver engaging portion at the other end thereof, a shank arranged between the cutting portion and the driver engaging portion. The shank is formed with a helical groove for discharging cuttings. The driver engaging portion has a hexagonal outer shape and is formed with a hexagonal hole and a recess at bottom of the hexagonal hole for receiving the tip of a driver. The cutting portion has a pointed tip and a substantially conical shape, a first recess formed by cutting off substantially a 180° section of the cutting portion as seen axially from the pointed tip with an edge in the rotational direction forming a cutting edge, and a second recess formed by cutting off substantially a 90° section of the remaining 180° section. The second recess is separated from the first recess by a thin-walled partitioning wall.

Abstract: The present invention provides a fastener, such as a screw or nut and tool designed in particular for use with an orthopedic implant system wherein the fastener has a multi-lobed torque driving recess. The recess has a central area bounded by equally spaced hemicircular grooves separated by internally projecting land having two sharp edges. The tool has a corresponding male shape, which in conjugation with the recess, is designed to achieve a controlled torque load with a minimized possibility of stripping the recess or of shearing the torque-driving tip from the tool.

Abstract: A sidewalk bolt is provided. The bolt includes a head portion, a threaded shaft portion extending perpendicularly outward from a first side of the head portion, and a socket head recess well formed within a second side of the head portion for use in driving the bolt. A depth of the recess well is greater than the width of the head portion between the first side and the second side.

Abstract: A drive socket for a male threaded fastener includes three rounded lobes of equal radius which are located equidistant from the center of the fastener and 120° apart from each other. The drive socket also includes three flat surfaces, each flat surface being located opposite one of the lobes and equidistant from the center of the fastener. Another embodiment of a drive socket includes a first set of three lobes and a second set of three lobes, each lobe being of equal radius and equidistant from the center of the fastener. The lobes of the first set are 120° apart and the lobes of the second set are also 120° apart and 60° apart from the lobes of the first set. Each of the lobes of the first set includes a flat surface which is adjacent and tangential to the radius portion of the lobe.

Abstract: A screw (1) is provided with a shank (3), a head (2) and a boring part (5). The shank (3) is provided with a thread (4). The head (2) has a shoulder (6) disposed at an axial distance (B) from the bearing face (12), while a portion (7) adjoining the shoulder on the shank side is provided with a tool drive (8). The head (2) of the screw can therefore be seized in axially secure manner by a tool in the region of the shoulder (6), and this tool can then simultaneously transmit the necessary torque in the region of the tool drive (8) as well.

Abstract: A fastener having a tamper-evident sleeve thereon. The fastener has a shank and a double-headed driving portion that is integrally formed with the shank. The double-headed portion includes an outer head for driving the fastener into a work piece or nut and an inner head for removing the fastener from an assembly. The sleeve is on the inner head and prevents a tool from being engaged with the sleeve for removal of the fastener without there resulting some indication that someone has removed or tried to remove the fastener.

Abstract: A combination sidewalk bolt is provided. The bolt includes a head portion, a threaded shaft portion extending perpendicularly outward from a first side of the head portion, a socket head recess well formed within a second side of the head portion for use in driving the bolt, and a slotted screwdriver slot provided in the second side of the head portion. A depth of the recess well is greater than the width of the head portion between the first side and the second side.

Abstract: A high-torque fastener having a threaded shaft and a star-shaped head is disclosed. The high-torque fastener is made of a resorbable or other non-magnetic material. A mating driver snugly fits around the star-shaped head of the fastener, to thereby apply torque to the perimeter of the star-shaped head. The driver can be made disposable, and the driver and fastener packaged together in a single, disposable assembly. Additionally, the driver can be color coded to indicate the size of the fastener which is pre-attached to the driver in the packaging.

Abstract: A screw retention device is disclosed having a clamping part and a hook part. The clamping part engages the head of a screw for securely retaining the screw. The hook part interacts with a surface of the component on which the screw is fastened to limit the rotation of the screw. The screw retention device is configured to be used with any known screw having a protruding head. In a preferred embodiment of the invention, the screw retention device is used with a serrated screw wherein the clamping part of the screw retention device includes a serrated portion which corresponds to and engages with the serrations on the serrated screw to securely grip the screw.

Abstract: A screw retention device is disclosed for maintaining at least a pair of screws in a substantially static position. The screw retention device preferably includes at least two clamping portions, each clamping portion defining a recess therein for receiving and securely retaining a screw. The clamping portions include a serrated surface extending circumferentially around an inside periphery of the clamping portion, surrounding the recess. The serrated surface of the clamping portion corresponds to and engages with a serrated surface on the screw to retain the screw. In a preferred embodiment of the invention, the screw retention device is press fitted onto the screws.

Abstract: A fastener for use with inch and metric wrenches has a body unitarily formed with at least one screwthread, a pair of concentric faceted tool-fitting regions of different sizes, and a step between the regions. One of the regions corresponds to a metric wrench size and the other of the regions corresponds to an inch wrench size. The screwthread and both regions are coaxial.

Abstract: Fasteners and devices and methods for placing fasteners in a workpiece are disclosed. More particularly, non-removable permanently-placeable fasteners for placement in a workpiece to hold elements thereof together, permanently-placeable but removable fasteners for placement in a workpiece to hold elements thereof together, headless removable one-way fastener inserter or heads by which the fasteners are placed, tools for permanently placing such fasteners, tools for removing certain of the fasteners and methods by which such fasteners are placed in, and in some cases removed from a workpiece.

Abstract: A high-torque fastener having a threaded shaft and a star-shaped head is disclosed. The high-torque fastener is made of a resorbable or other non-magnetic material. A mating driver snugly fits around the star-shaped head of the fastener, to thereby apply torque to the perimeter of the star-shaped head. The driver can be made disposable, and the driver and fastener packaged together in a single, disposable assembly. Additionally, the driver can be color coded to indicate the size of the fastener which is pre-attached to the driver in the packaging.

Abstract: The present invention provides a novel fastener having a tamper indicating tool engaging drive head. The fastener has a shank including a threaded shank portion. The fastener also has a double-headed driving portion that is integrally formed with the shank. The double-headed portion includes an outer head for driving the fastener into a work piece or nut and an inner head for removing the fastener from an assembly. The inner head is joined to the outer head such that the inner head is positioned between the outer head and the shank. Extending portions extend from tool engaging surfaces of the inner head. In use, the fastener is driven into an assembly via a proper tool that engages with the outer head. The outer head shears off the fastener when the desired torque is achieved, leaving only the shank within the assembly and the inner head exposed.

Abstract: A combination sidewalk bolt is provided. The bolt includes a head portion, a threaded shaft portion extending perpendicularly outward from a first side of the head portion, a Phillips head recess well formed within a second side of the head portion for use in driving the bolt, and a slotted screwdriver slot provided in the second side of the head portion. A depth of the recess well is greater than the width of the head portion between the first side and the second side.

Abstract: A fastening assembly for fastening a first member to a second member comprising at least one threaded fastener having a head at one end thereof, the head having engagement surfaces for a tool, a threaded shank, the other end of the shank having engagement surfaces for a tool, at least one receiving bore in the first member into which the threaded shank is threaded in a pre-mounted state from one end thereof, with the head being spaced from the associated surface of the first member, the second member being preferably of thin sheet material and having at least one elongated opening, the opening having a first portion adapted to allow the entrance of head and a smaller portion adapted to accommodate the shank while the head grips behind the edge of the opening.

Abstract: The present disclosure relates to a clamp for sealing a lap joint formed by a first pipe inserted within a second pipe. The clamp includes a strap having a concave inner curvature that curves about a central axis. The strap includes a first axial end positioned opposite from a second axial end. A first axial portion of the strap is positioned at the first axial end, and a second axial portion of the strap is positioned at the second axial end. The first axial portion has a cylindrical inner surface adapted to provide a seal about the first pipe, and the second axial portion has a cylindrical inner surface adapted to form a seal about the second pipe. A radial in-step connects the first and second axial portions. The radial in-step provides a diameter transition between an inner diameter D1 of the first axial portion and an inner diameter D2 of the second axial portion such that the inner diameter D1 is larger than the inner diameter D2.