Abstract: This publication describes techniques and apparatuses for releasably attaching an object (e.g., a wire tray) to a substrate. Current apparatuses generally do not enable the removal of an attached wire tray from a substrate without first removing an insert from a mounting stud extending from the substrate. The disclosed techniques and apparatuses are configured to permit the removal of an attached wire tray from a substrate without first removing an insert from a mounting stud extending from the substrate.

Abstract: A rivet for fastening workpiece members, the rivet including a body comprising a shank extending in a first, longitudinal direction and a head extending in a second, substantially transversal direction, a bore being defined through the shank and the head of the body; and, a stem comprising a main longitudinal portion arranged for insertion into said bore, and an enlarged portion arranged for radially expanding the shank when the enlarged portion is forced into said bore to fasten the workpiece members; the rivet being configured for insertion into respective apertures formed in the workpiece members; and the rivet being further configured such that when the workpiece members are fastened, the head of the body of the rivet is displaced relative to the shank to engage with the stem to lock the stem in place relative to the body and/or the workpiece members.

Abstract: A pin and ring-type plug assembly for plugging a heat exchanger tube to provide a leak resistant seal is provided. The plug assembly is designed such that it can be used to form a high-pressure seal relative to a wide of range of tube inner diameters. The angle of taper of the pin varies along a length of the pin such that the angle of taper is steepest at or adjacent a nose section of the pin and is shallowest at or adjacent an end section of the pin.

Abstract: This publication describes techniques and apparatuses for releasably attaching an object (e.g., a wire tray) to a substrate. Current apparatuses generally do not enable the removal of an attached wire tray from a substrate without first removing an insert from a mounting stud extending from the substrate. The disclosed techniques and apparatuses are configured to permit the removal of an attached wire tray from a substrate without first removing an insert from a mounting stud extending from the substrate.

Abstract: A tool for installing a blind fastener. The tool includes a retention member and a gripping member that defines a longitudinal axis and is moveable relative to the retention member along the longitudinal axis, the gripping member further defining a receiving cavity that is elongated along the longitudinal axis, an axial opening into the receiving cavity, and a radial opening into the receiving cavity. The tool also includes a contact element at least partially received in the radial opening and a locking collar moveable relative to the gripping member along the longitudinal axis between at least a first position and a second position. In the first position the locking collar engages the contact element and urges at least a portion of the contact element into the receiving cavity. In the second position the locking collar is disengaged from the contact element.

Abstract: An insert to be crimped on a support includes a body having a shank extending along a longitudinal axis and including a crimping section configured to deform into a crimping bead to crimp the insert on the support, and a flange presenting a surface facing the crimping section and extending along an axis perpendicular to the longitudinal axis, the flange having a constant thickness and presenting a fold forming a groove situated on the surface and designed to receive a seal. A fixing part includes the insert and a seal housed in the groove of the insert, and a fixing assembly includes the fixing part and a support on which the fixing part is crimped.

Abstract: A blind fastener has a sleeve and a pin. The sleeve has a shank with a shank bore and a head with a head bore smaller than the shank bore. The pin has a pin installation portion with a proximal end portion and a distal end portion. The pin also has a breakaway portion with a pin grip, and a pin break groove between the installation portion and the breakaway portion. The pin further has a grip portion at the proximal end portion of the pin installation portion and directly adjacent to the pin break groove. In a pre-installation configuration, the grip portion is in the sleeve bore. In an installation configuration, the grip portion is in the head bore and forms a friction fit with the head bore to prevent the installed sleeve from inadvertently coming free of the installed pin.

Abstract: Disclosed is a fastener that includes a nut with a threaded bore that includes a head on one end having three recesses, a cylindrical outer surface and a tapered ramp on the other end, a bolt that includes a head, a threaded portion engaged with the threaded bore, a recess next to the bolt head and an enlarged shank between the threads and the recess, where the outer diameter of the recess is smaller than a major diameter of the threaded bore of the nut and where an outer diameter of the shank is larger than a major diameter of the bolt threads, and a sleeve with a unthreaded bore positioned between the tapered ramp and the bolt head with one end crimped into the recess such that the internal diameter of the crimped sleeve bore is smaller than the major diameter of the threads on the bolt.

Abstract: A male luer connector includes a body having a first end configured to be connected to a fluid line, a second end opposed to the first end, and a body longitudinal axis. The second end is configured to be inserted into and form a luer slip connection with a female luer connector. The male luer connector also includes a locking collar that is connected to the body in a manner such that the locking collar rotates about the longitudinal axis. In some cases, the body second end does not protrude beyond a plane that is transverse to the longitudinal axis and that includes an end face of the locking collar, and/or when male and female connectors are engaged, the locking collar engages an outer surface of the female fluid line connector and is deformed by the engagement.

Abstract: A door frame assembly includes integral shim screws in the vertical jambs that facilitate installation of the assembly into a rough opening or doorway. The vertical frame jambs have one or more holes therethrough. Shim screws are positioned in those apertures and are adjustably extendable outwardly therefrom to engage a rough opening to assist in fixing the frame in that opening.

Abstract: An instrument assembly includes a downtube having a tubular body with a proximal end and a distal end. In one embodiment, the proximal end forms an opening for receiving a surgical tool, and the distal end forms at least two attachment members for attaching to a bone anchor. The tubular body forms a hollow passage extending from the proximal end to the distal end. The assembly includes a key for insertion into the proximal end of the downtube to attach the downtube to a bone anchor. The key includes an engagement end configured to engage the at least two attachment members when the key is inserted into the downtube. The key is rotatable within the tubular body between a clamping orientation and a releasing orientation.

Abstract: A power converter includes a case body provided with a device main body part having a power conversion part accommodated therein, a lid member covering an aperture of the case body, a first substrate fixed to the case body, a second substrate fixed to the lid member, the first substrate and the second substrate being fixed therein and a connection member electrically connecting the first substrate and the second substrate.

Abstract: A cylinder for storing a plurality of rings to be crimped, said cylinder comprising a base body including a distribution outlet, a main cylindrical body mounted so that it can rotate along a cylinder axis relative to said base body in a plurality of angular positions, said main cylindrical body comprising a plurality of sheaths which are parallel to one another and each suitable for accommodating a plurality of rings, each sheath being arranged so as to lead to said distribution outlet of said base body for a predetermined angular position of said main cylindrical body.

Abstract: Disclosed is a coupling member that enables a joint between a wooden member and a mating member to absorb vibration energy, and a method for producing the same and a joint structure using the same. The metal coupling member is embedded in the wooden member. The wooden member is connected with a mating member by the coupling member. The coupling member includes a metal rod-like main body portion to be embedded in the wooden member, and an inner rod portion protruding from the main body portion. The inner rod portion axially extends from a protruding portion thereof to a predetermined depth in the main body portion, has a periphery separated from the main body portion to allow axial displacement of the inner rod portion relative to the main body portion, and is integrally connected to the main body portion at the deepest part thereof.

Abstract: A sleeve interference fastener including a conformable sleeve, wherein the conformable sleeve is comprised of at least one first material having a hardness of X, and a pin member, wherein the pin member is comprised of at least one second material having a hardness of Y, wherein X is sufficiently less than Y so that, in an installed position of an interference fit, at least a portion of the at least one first material of the conformable sleeve conforms to a contour of an inner surface of a hole of a composite structure so as to create a continuous electrical contact at an interface between the inner surface of the hole of the composite structure and the conformable sleeve.

Abstract: A method and system for installing rivets is disclosed. The method involves positioning a rivet through a structure to be joined. The method further involves positioning a first rivet gun on a first side of the rivet and positioning a second rivet gun on a second side of the rivet. The method also involves synchronizing firing of the first and second rivet guns, so as to cancel forces that otherwise would propagate into the structure during installation of the rivet.

Abstract: A fastener includes a body having a cylindrical passage formed through a central portion of the body and a tapered ramp disposed at an end of the body and a corebolt disposed within the passage formed by the body. The fastener further includes a sleeve movably disposed over the corebolt and adjacent the tapered ramp of the body. The sleeve includes a bore extending between first and second ends of the sleeve and a taper extending inwardly from the second end of the sleeve toward the first end of the sleeve, the second end of the sleeve being adjacent the tapered ramp of the body. The sleeve further includes a weakened interior region disposed between the taper and the first end of the sleeve, the weakened interior region being adapted to bulb outwardly when the sleeve is compressed against a workpiece.

Abstract: A lock bolt collar comprises a shank having a first end, a second end opposite the first end, a through-bore extending from the first end to the second end, an inner wall having an internal bead located proximate to the first end of the shank and extending circumferentially and inwardly into the through-bore. The bead includes a first inner diameter and an extended portion extending from the bead and to a point proximate to the second end, the extended portion including a second inner diameter, where the second inner diameter is greater than the first inner diameter.

Abstract: A self-drilling expansion fastener is integrally formed of a sheet metal material for locking two or more sheet workpieces together, and includes an expansion structure and a drill structure. The expansion structure has a plurality of internal threads and force-distributing bars. The drill structure has a chip guard for covering a head of the expansion structure, and a drill forward projected from the chip guar for self-drilling a hole. When an externally threaded element is screwed into the expansion structure to mesh with the internal threads, the force-distributing bars are brought to expand outward and are finally compressed into a folded state to thereby tightly lock the sheet workpieces to one another. A method of forming the self-drilling expansion fastener is also disclosed.

Abstract: A fastener having a pin member and a sleeve. The pin includes a head, a pin tail portion, and a locking portion with a plurality of crests and roots. Each of the crests includes a first diameter, the first diameters sequentially increase along the locking portion towards the head, while the roots include a second diameter, the second diameters sequentially decrease towards the head. The sleeve has a head and a tubular portion which is deformed into a bulb that engages a workpiece. The tubular portion of the sleeve locks onto the crests and the pintail portion of the pin member breaks off at one of the grooves located substantially flush with the head of the sleeve.

Abstract: A rivet includes a pin member having a head and a lock groove, and a lock ring having a flange. The flange of the lock ring is swaged into the lock groove of the pin member and transformed to a bead that engages the lock groove, and a portion of an outer surface of the lock ring deforms and is rotated inwardly. The rivet is installed within a structure such that the head of the pin member is flush with an outer surface of a panel and the portion of the outer surface of the lock ring is flush with an outer surface of another panel. The pin member includes a frangible portion that breaks off when the rivet is installed.

Abstract: A fastener comprises a body having an enlarged head at a first end, a tapered ramp at a second end, a cylindrical shank disposed between the enlarged head and the tapered ramp, and a passage extending between the first and second ends and including threads. The fastener further includes a generally cylindrical corebolt disposed within the passage of the body and having an enlarged head, a breaking groove, and a stop shoulder that is configured to cause an abrupt increase in resistance to threading the corebolt into the body when the breaking groove is substantially flush with an outer surface of the enlarged head. A grip compensator is disposed on the corebolt in abutment with the enlarged head of the corebolt. A deformable sleeve is movably disposed over a portion of the corebolt and disposed between the grip compensator and the tapered ramp of the body.

Abstract: A tacking fastener for securing workpieces together to form a temporary assembly is provided that includes a stem and a sleeve. The stem includes a proximal end portion, a central portion, and a distal end portion. The stem further includes a head disposed at the proximal end portion, the head defining a distal face having a gripping feature. The sleeve includes a flange disposed at the distal end portion, the flange defining a proximal face having a gripping feature. The sleeve is disposed around the stem and configured to form a tacking rivet upon installation of the tacking fastener. The sleeve is plastically deformed during installation to form a plurality of bulbs, thereby being capable of securing workpieces of varying grip length. The stem and the tacking rivet remain within the workpieces after the workpieces are secured.

Abstract: A blind rivet made of plastic, the shank of the body has a first region located between the head and the foot end, and the first region has a reduced first wall thickness. Within the first region is located a second region with a second wall thickness further reduced as compared to the first region. The first and second regions are arranged such that, as a result of the rivet setting process, the wall of the shank forms a roll fold with an annular bead that is pressed axially against the blind side of the workpiece.

Abstract: A variable grip blind rivet has a rivet body with a first shank adapted to be inserted into a hole in a workpiece and having an axial bore, and a flange at a first end of the first shank for abutting the workpiece when the first shank is inserted into the hole in the workpiece. A mandrel has a head, for engaging a second end of the first shank, and a second shank adapted to extend through the axial bore. The head has an abutment portion for abutting the first end of the first shank. At least one protrusion adjacent the abutment portion defines a recess for receiving the first end of the first shank during setting of the rivet.

Abstract: A rivet stud has a rivet body with an elongated shank, a flange, and an axial bore in which is located a tension mandrel, which has a mandrel shank with a drawing end projecting out of a head end of the rivet body that is separable from the mandrel shank at a predetermined breaking point and which has a mandrel head that is supported on a foot end of the rivet body. The mandrel shank is provided with locking means that secure it in the rivet body after setting of the rivet stud, and the predetermined breaking point is located such that the breaking point lies inside the bore of the rivet body after setting of the rivet stud. Located on the mandrel head is a mounting stud that projects from the mandrel head on the side opposite the mandrel shank.

Abstract: A fastener having a pin member and a sleeve. The pin includes a head, a pin tail portion, and a locking portion with a plurality of crests and roots. Each of the crests includes a first diameter, the first diameters sequentially increase along the locking portion towards the head, while the roots include a second diameter, the second diameters sequentially decrease towards the head. The sleeve has a head and a tubular portion which is deformed into a bulb that engages a workpiece. The tubular portion of the sleeve locks onto the crests and the pintail portion of the pin member breaks off at one of the grooves located substantially flush with the head of the sleeve.

Abstract: In order to form a reliable blind rivet connection in the case of a joined connection between two components having at least one laminate component, without the risk of delamination of the laminate component, a two-layer structure of the rivet sleeve of the blind rivet is provided. The inner layer is formed in this case of a higher strength material, in particular of stainless steel. The outer layer is formed of a softer material, in particular plastics material.

Abstract: A head is formed so that the maximum diameter portion as viewed from the front is arranged in a different position axially with respect to the maximum diameter portion as viewed from the side. The horizontal cross-section of the head is such that a first ellipse is formed in the maximum diameter portion, and a second ellipse is formed in the maximum diameter portion with the long axis perpendicular to the long axis of the first ellipse. The horizontal cross-sectional shape of the head is gradually changed in the axial direction so as to continue from the first ellipse to the second ellipse. Each one of the horizontal cross-sections has the same circumferential length at different axial positions on the head.

Abstract: A method of operating with a rivet is for the coupling and the tack riveting together of a first element and a second element. The method comprises positioning the rivet such that the rivet traverses two substantially coaxial openings arranged in the first and second elements to be assembled; pulling the mandrel to form a bulb on the second end; and resuming pulling of the mandrel, to cause a rupture of the sleeve at the bulb so as to permit removal, by way of the external surface of the first element, of the mandrel and of a first portion of the sleeve as well as the falling away of the portion of the bulb remaining on the external surface of the second element.

Abstract: A blind rivet includes a hollow rivet body having a longitudinally extending indented groove. The groove may be shaped to impart rivet setting characteristics that may be varied to provide desirable fastening characteristics for joints in a number of industries. The shape of the indentation on the rivet body may be varied to cause a portion of the rivet body to collapse and form a secondary head at a predetermined longitudinal location.

Abstract: Self-tapping blind rivet (10) having a mandrel (12) carrying a hole-forming tip (16) at its end facing the workpiece, wherein the tip (16) is performed as an apparatus for drilling the rivet's own placing hole, wherein a positive or non-positive connection is provided between the mandrel (12) of the rivet and the rivet shank (18) and, wherein a force application point (26) for a tool is provided at or in the rivet head (20), and a method for placing such a blind rivet.

Abstract: A rivet stud has a rivet body with an elongated shank, a flange, and an axial bore in which is located a tension mandrel, which has a mandrel shank with a drawing end projecting out of a head end of the rivet body that is separable from the mandrel shank at a predetermined breaking point and which has a mandrel head that is supported on a foot end of the rivet body. The mandrel shank is provided with locking means that secure it in the rivet body after setting of the rivet stud, and the predetermined breaking point is located such that the breaking point lies inside the bore of the rivet body after setting of the rivet stud. Located on the mandrel head is a mounting stud that projects from the mandrel head on the side opposite the mandrel shank.

Abstract: A blind rivet comprises a sleeve, a body, and a mandrel. The sleeve includes a barrel with a hexagonal cross-section, a flange, and a through-hole. The rivet body includes a base, a barrel with slits extending in the axial direction, and a through-hole. The mandrel includes an elongated stem and a head. During the setting process, the barrel of the rivet body is pushed open by the head of the mandrel, and the objects to be fastened are fastened between the opened portion of the barrel and the flange of the sleeve. The mandrel is then pulled further and the polygonal vertices of the sleeve barrel are compressed by a round squeezing hole in a nosepiece. The compression of the sleeve barrel forces the inner circumference of the barrel into non-sliding engagement with the mandrel.

Abstract: A blind fastener including a pull-type core bolt having a shank with a head, and a sleeve having an elongated body with a head, and a tapered notch formed within an exterior surface thereof and defined by a tapered portion having a slope and a frictional enhanced surface. The core bolt is installed within the sleeve. During installation of the fastener within the plurality of work pieces, an axial force is applied to the core bolt the head of the core bolt engages the sleeve, and a bulb is formed on the elongated body of the sleeve, the bulb defining a portion of a bulbed portion. When a selected axial force is reached, the bulbed portion separates from the elongated body and engages axially the tapered portion of the sleeve, increasing the diameter of the bulb which engages a blind side of one of the work pieces.

Abstract: A blind fixation device for attaching an assembly of a pre-drilled member set that includes a rod defining a traction mandrel, a first bushing, and a second deformation brushing. The second deformation bushing is capable of deformation on an inaccessible side of the set of pre-drilled members between the head of the mandrel rod and the end portion of the first bushing. The first bushing is capable of bearing on the accessible side surface of the set of pre-drilled members to be assembled, and is capable of radial deformation so as to come in close contact with the drilling profile of at least one pre-drilled member when, upon assembly, the portion of the mandrel rod initially in the second bushing enters the first bushing.

Abstract: A fastener adapted to pass through aligned holes through workpieces is disclosed. The fastener includes a pin member having a transition portion wherein the diameter of the transition portion decreases radially as it extends from the smooth cylindrical shank portion to the threaded portion. The fastener may also comprise a sleeve member and a clamping means. The clamping means includes a collar, a nut, or any other possible clamping means. In exemplary embodiments, the workpieces can be formed with a plurality of materials, the materials including composite, metallic, or composite/metallic structures, any combination thereof. In particular embodiments, the fastener has interference capability of 0.0005 to 0.0100 inches in composite structures without risk of composite delamination or damage. As a result of the fastener interference, gaps between the fastener and the structure are eliminated thereby providing good electrical conductivity between components.

Abstract: A variable grip blind rivet has a rivet body with a first shank adapted to be inserted into a hole in a workpiece and having an axial bore, and a flange at a first end of the first shank for abutting the workpiece when the first shank is inserted into the hole in the workpiece. A mandrel has a head, for engaging a second end of the first shank, and a second shank adapted to extend through the axial bore. The head has an abutment portion for abutting the first end of the first shank. At least one protrusion adjacent the abutment portion defines a recess for receiving the first end of the first shank during setting of the rivet.

Abstract: A sealing plug for sealing a hole in a wall, which sealing plug is insertable into the hole by access from only one side thereof, which sealing plug comprises: a radially expandable body which is radially expandable by access thereto from only one end thereof, and a sealing cap which covers the other end of the expandable body and extends therefrom along the exterior of the length of the body, the sealing cap being of a material which is fluid resistant; whereby, when the sealing plug has been inserted in the hole and has been radially expanded so that at least part of the sealing cap adjacent the wall of the hole expands and engages therewith, the sealing cap is secured in the hole with the sealing cap sealing the plug body against access thereto from outside the cap.

Abstract: At least one embodiment generally relates to an installation assembly for an opening in a workpiece that includes a swaged collar, an inner member, and an outer member. The swaged collar has a first end, a second end, and a main body extending between the first end and the second end. The main body includes an inner surface defining a passageway through the collar. The inner member has a mandrel section for expanding the outer member. The inner member is used to expand the outer member and to keep the outer member in an expanded state.

Abstract: A blind rivet made of plastic, the shank of the body has a first region located between the head and the foot end, and the first region has a reduced first wall thickness. Within the first region is located a second region with a second wall thickness further reduced as compared to the first region. The first and second regions are arranged such that, as a result of the rivet setting process, the wall of the shank forms a roll fold with an annular bead that is pressed axially against the blind side of the workpiece.

Abstract: A fastener, capable of securing work pieces accessible from only one side, is provided. The blind fastener includes a deformable sleeve and a pin, the pin having a main body section and a tail section. The main body section includes a shear load bearing section integrally connected to a lock collar engagement section on a first end and a pin stalk section on a second end, the pin stalk section integrally connected to a series of pin sleeve integrating grooves. The tail section is integrally connected between the main body, via a break notch, and a series of serrations. The sleeve includes a hollow tubular shank having a first sleeve end and a second sleeve end, where the first sleeve end has a sleeve head having an opening for receiving the main body section. At all times during assembly of the fastener, the series of serrations remain outside the sleeve, never passing through the sleeve.

Abstract: Disclosed are several clamps and a method for installing the clamps through at least two work pieces from one side. The clamps include a shank, a spacer, a core bolt and an expander. The shank and expander are keyed to together with the expander engaged on the core bolt such that rotation of the core bolt can bulb the expander to form a clamp surface on the blind side of the work pieces. The shank and spacer are temporarily held apart until the expander is bulbed wherein the shank is allowed to enter the spacer to clamp the work pieces. Subsequent over torque of the core bolts fractures a weakened portion of the core bolt permitting removal of the clamps when desired.

Abstract: A variable grip blind rivet includes a tubular rivet body and a mandrel. The rivet body has a first shank, insertable into a hole in a workpiece, and a flange at a first end of the first shank for abutting the workpiece when so inserted. The mandrel has a head, for engaging a second end of the first shank, and a second shank adapted to extend through the axial bore of the rivet body. The head has an abutment portion for abutting the first end of the first shank, and the second shank has a first reduced diameter portion adapted to break when a predetermined tensile is loaded applied. At least one protrusion adjacent the abutment portion defines a recess for receiving the first end of the first shank during setting of the rivet.

Abstract: A blind rivet for joining components made of plastic has a hollow rivet body with an elongated shank and a flange and, located in the bore of the rivet body, a mandrel with a mandrel shank, a drawing end, and a mandrel head. The shank of the rivet body has a first section adjoining the flange and a second section adjacent thereto. The second section is designed to form a flange that lies flat against the component located on the inaccessible side. The strength of the first section is increased with respect to the strength of the second section in such a manner that the outside diameter of the first section does not increase or increases only slightly during setting of the blind rivet.

Abstract: A rivet stud has a rivet body with an elongated shank, a flange, and an axial bore in which is located a tension mandrel, which has a mandrel shank with a drawing end projecting out of a head end of the rivet body that is separable from the mandrel shank at a predetermined breaking point and which has a mandrel head that is supported on a foot end of the rivet body. The mandrel shank is provided with locking means that secure it in the rivet body after setting of the rivet stud, and the predetermined breaking point is located such that the breaking point lies inside the bore of the rivet body after setting of the rivet stud. Located on the mandrel head is a mounting stud that projects from the mandrel head on the side opposite the mandrel shank.

Abstract: A blind rivet design has an exposed mandrel portion modified from the conventional and standardized mandrel to reduce amount and cost of materials required to produce the mandrel, while also minimizing costs related to production, use, and spent mandrel disposal, all while still making use of conventional riveting tools for rivet setting and maintaining rivet performance. The blind rivet also facilitates feeding of a shortened spent mandrel through conventional riveting tools and into mandrel collection devices.

Abstract: A blind rivet element includes a setting head attached to one head of a shank that is smaller in diameter than the setting head and has an opposite end with an internal female thread or a receptacle for a threaded bolt as well as a deformation section disposed axially therebetween. The blind rivet is inelastically deformed from an unset condition to a set condition thereby forming a radially outwardly protruding bead which serves to fasten the blind rivet element to a workpiece. The deformation section includes a void that interrupts the bead and defines a non-arcuate edge along that portion of the bead disposed adjacent to the void.

Abstract: A mounting/assembly element rivet bush having a deformable first end for insert through items to be connected and a second end for mounting a nut. A draw tool having a break zone is located in the first end of the rivet bush, and the second end of the rivet bush is provided with a non-cylindrical internal cross section which cooperates with an insertion tool, such as an Allen wrench. When the mounting/assembly element is held fast in the items to be connected, the part of the break zone of the draw tool for the deformation of the rivet bush is lying in the deformable first end of the rivet bush. A counter-hold for torsion forces which arise with the dismounting and remounting of the nut is produced with the insertion tool thereby achieving a considerably greater tightening effect and also ensuring that the mounting/assembly element can be reused.

Abstract: A mandrel has an anti-dropping-off portion that is formed between a head and a breakable portion thereof. In the anti-dropping-off portion, a plurality of latching ridges is formed which have peaks that protrude outwardly in the radial direction and frictionally engage with the inner wall surface of a sleeve. The latching ridges are formed in the outer surface of the portion of the mandrel that is between the head and breakable portion thereof, so as to be diagonal relative to the circumferential direction of the outer surface of the mandrel and to cross each other, with the peaks thereof formed in a twill pattern protruding out from the outer surface of that mandrel portion.