Abstract: A locknut includes a nut body having a threaded through opening therein extending between a first end and a second end. A pocket is defined within the second end of the nut body. A spring member disposed within the pocket includes a pair of leg members joined together by an apex member so that the leg members are disposed in substantially parallel, spaced-apart relation to one another. The leg members define locking surfaces thereon so that when the externally threaded member is threaded into the threaded through opening defined by the nut body the externally threaded member contacts the locking surfaces. The locking surfaces exert pressure on the externally threaded member at substantially opposed radial locations to develop a locking force between the nut body and the externally threaded member.

Abstract: An embodiment is an apparatus, such as a plasma chamber. The apparatus includes chamber walls and a chamber window defining an enclosed space. A chamber window is disposed between a plasma antenna and a substrate support. A gas delivery source is mechanically coupled to the chamber window. The gas delivery source comprises a gas injector having a passageway, a window at a first end of the passageway, and a nozzle at a second end of the passageway. The nozzle of the gas delivery source is disposed in the enclosed space. A fastening device is mechanically coupled to the gas delivery source. The fastening device is adjustable to adjust a sealing force against the gas injector.

Abstract: A method for preloading a bearing includes releasably, threadably, and directly attaching an attaching member to a circumferential outside surface of an exposed end of a threaded shaft of an axle or spindle. A frame is axially separated from, and coupled to, the attaching member. A plurality of extensions extends from the frame axially past the attaching member toward the wheel hub assembly. An adjustment mechanism moves the frame and the plurality of extensions axially towards the wheel hub assembly to contact the wheel hub assembly and/or the bearing to apply a preload to the bearing within the wheel hub assembly.

Abstract: An actuator includes a threaded spindle and an internally threaded component screwed onto the threaded spindle. The component includes a plastic element having a first axial end and a second axial end and an interior having a width and a radially inwardly projecting flange at the first axial end, and the flange has an inner diameter less than the width of the interior. A metal element, such as a nut, is fixedly mounted in the interior of the plastic element, and the internal thread of the nut has a maximum diameter greater than the inner diameter of the flange.

Abstract: A device that prevents the self-adjustment of a leveling glide for the tubular legs of various types of furniture, including tables and chairs, is disclosed. The device comprises a threaded insert for a furniture leveling assembly that includes a polymeric washer secured to the bottom of the threaded insert. The polymeric washer is aligned with the axis of the internally threaded of the threaded insert and has a hole diameter that is smaller than the diameter of the externally threaded stem of the leveling glide.

Abstract: An improved locking nut and sealing washer for use with a threaded bolt. The locking nut has a flange. The sealing washer is attached to an elastomer and has retaining means provided therein. When the locking nut is seated on the sealing washer, a removable retaining insert may be manipulated to be received within the retaining means. Thereafter, when force is applied to the locking nut to move the locking nut in a first direction along the threaded bolt, the flange pushes against the sealing washer to push the sealing washer in the same direction and, when force is applied to the locking nut in an opposing direction along the threaded bolt, the flange pushes against the retaining insert to push the sealing washer in the same direction.

Abstract: Implants, instruments, and methods are presented for fixing adjacent bone portions to promote fusion of the bone portions.

Abstract: A fence support system includes a catch member having a protrusion and a retainer member having an aperture configured to receive the protrusion. A method of supporting an apertured fence material includes providing a catch member comprising a protrusion extending from a catch plate of the catch member, providing a retainer member comprising an aperture configured to receive the protrusion of the catch member, and capturing an apertured fence material between the catch member and the retainer member.

Abstract: A connector seal device includes, in one embodiment, a seal body extendable along an axis and configured to receive an end of a coupler. The coupler is configured to be rotatably coupled to a coaxial cable connector, and the seal body is configured to engage a portion of the coupler to establish a first environmental seal between the seal body and the coupler. The connector seal device also includes a seal neck integral with the seal body configured to extend along the axis beyond the end of the coupler. The seal neck is configured to engage an interface port to establish a second environmental seal between the seal neck and the interface port.

Abstract: A turbocharger including, a turbine wheel (10), a shaft (111) attached to the turbine wheel (10), and a compressor wheel (132) disposed on the shaft (111) opposite the turbine wheel (10). The compressor wheel (132) includes a back wall (134) and an axial bore (137) and a pilot washer (150) is located adjacent the compressor wheel back wall (134). The pilot washer (150) has an inner diameter (162) and an outer diameter (160), and includes a conical pilot ring (154) that extends into the axial bore (137) of the compressor wheel (132). The pilot washer (150) includes a slit (164) extending from the inner diameter (162) to the outer diameter (160). A nut (113) is threaded to the shaft (111) and is operative to provide an axial clamping force on the compressor wheel (132), thereby causing the pilot washer (150) to contract onto the shaft (111) as the pilot ring (154) extends into the bore (137).

Abstract: A connector seal device includes, in one embodiment, a seal body extendable along an axis and configured to receive an end of a coupler. The coupler is configured to be rotatably coupled to a coaxial cable connector, and the seal body is configured to engage a portion of the coupler to establish a first environmental seal between the seal body and the coupler. The connector seal device also includes a seal neck integral with the seal body configured to extend along the axis beyond the end of the coupler. The seal neck is configured to engage an interface port to establish a second environmental seal between the seal neck and the interface port.

Abstract: A fluid pressure cylinder includes a cylinder tube, a piston and a solid piston rod. The piston rod includes a head-side passage defined by a head-side shaft hole extending in an axial direction, a head-side outer hole open on a part projecting from the cylinder tube and a head-side inner hole open to a head-side chamber and allowing communication between a head-side chamber and a fluid pressure source, and a bottom-side passage allowing communication between a bottom-side chamber and the fluid pressure source. The head-side shaft hole includes an opening end and a tip formed inside the piston rod. The opening end of the head-side shaft hole is sealed by a sealing member.

Abstract: An axle nut for preloading a bearing is provided. The axle nut may be used to apply and monitor preload on a bearing or bearing assembly. The axle nut includes a cylindrical body having a first end, a second end having a face adapted to bear against a surface, a longitudinal axis, and an outer surface engagable by a tool; a threaded through-hole directed substantially along the longitudinal axis of the cylindrical body; and at least one recess in the face of the second end of the cylindrical body, the at least one recess adapted to expose at least a portion of the surface the face bears against. The first end of the axle may comprise a nut locking mechanism, for example, the nut locking mechanism may include a counter bore having a plurality of internal projections, such as, gear or spline teeth.

Abstract: A prevailing torque locknut having a nut body, a locking band, and a retainer. The nut body includes a threaded portion and an unthreaded counterbore. The locking includes a coil portion and first and second tangs extending tangentially from the coil portion. The locking band is located within the counterbore, and the first and second tangs engage the counterbore sidewall to prevent relative rotation of the locking band within the nut body. The retainer is swaged into the nut body to secure the locking band within the nut body.

Abstract: A screw hole seal structure seals a screw hole (13) in molding a fiber-reinforced resin member (1) in which an insert member (4) provided with the screw hole (13) is integrally incorporated. In the structure, a screw member (5) is tightened in the screw hole (13). In the structure, an elastic seal member (6) is compressed within the screw hole (13), in an axial direction of the screw member (5), and is therefore deformed radially outwards by compression force that is created by tightening of the screw member (5), and an air-tight state of the screw hole (13) is maintained by deformation of the elastic seal member (6).

Abstract: A threaded joint includes a flange, a nut and a flexible seal. The flange, the nut and the flexible seal have threads respective inner surfaces, the threads having shapes complementary to threads on an outer surface of a stem. The flange is configured to allow the stem to move by rotation through the flange. The nut and the flexible seal are configured to move by rotation relative to the stem. The flange has a counter bore and the nut has a groove. The flexible seal has a first portion configured to fill the counter bore in the flange, and a second portion configured to fill the groove of the nut.

Abstract: The present invention is directed to a retention element for retaining first and second components in assembled relationship. The first component comprises a body having first and second external surfaces and an inner wall defining an aperture extending through the body, and the second component comprises a longitudinal member having a size and configuration to permit insertion within said aperture to thereby assemble the components. The retention element comprises: an elastromeric protuberance extending into the aperture from a base adhering to the inner wall to a distal edge which spans a portion of the aperture. The protuberance also has an inside wall and an outside wall which meet at the distal edge and together define a flexible free end.

Abstract: An inset panel fastener is provided primarily for honeycomb substrates, such as those employed in the aircraft industry. The inset panel fastener includes a plastic body portion and a metal female threaded nut positioned within the body. The body includes a cylindrical barrel shape having a top and a bottom. A bore extends through the body from the top to form an opening for receipt of a male fastener. The metal nut has locking threads and is positioned in body's bore at the body's top proximal extremity. The body further includes non-locking plastic female threads integrally formed into said body's bore. The plastic female threads have the same diameter as the metal threads and are immediately adjacent to the metal threads so as to form continuous threads for permitting receipt of a male threaded fastener. The metal female threads are locking threads to provide a locking action for locking a male fastener to the inset panel fastener.

Abstract: A nut having an injection-molded insert or delay stopper is threaded onto an end of an anchor. A capsule containing a resin component and a catalyst component and the other end of the anchor are positioned in a bore hole in a mine roof, mine wall, side of a hill, concrete wall, or concrete floor. The threaded end of the nut contacts the insert and rotation of the nut rotates the anchor, breaking the capsule and mixing the components. After the components set, increased torque is applied to fracture the insert and move the nut up the threaded end of the shaft against roof stabilizing components on the shaft.

Abstract: A tee-nut fastener which includes a nylon locking ring located distally from the entrance to a passageway ensures proper fastening upon coupling with a threaded stud. The tee-nut is used use in combination with a track for efficient delivery. The track comprises an upper guide spaced apart relatively farther than a lower guide. The process for making the tee nut uses a cold heading process. The tee-nut includes a flange having an upper portion and a lower portion. A shank extends perpendicularly from the upper portion and a head extends oppositely from the shank and perpendicularly from the lower portion. The flange includes at least two teeth extending in the direction of the shank and a passageway through the shank, flange and head. The passageway includes a bore countersunk at both ends thereof, a cavity, and threads therein.

Abstract: A hydraulic piston and cylinder unit comprising the combination of a cylinder assembly defining a cylindrical chamber, a piston member mounted in the cylindrical chamber for reciprocating movement therein in response to movement of hydraulic fluid under pressure into and out of the chamber, and a piston rod member connected to the piston member for movement therewith and extending from one end of cylinder assembly. The members have meshing threads thereon configured to be meshingly interengaged when the members are rotationally moved into an assembled position relative to one another in one direction.

Abstract: A lock nut system includes a molded nut having a plurality of teeth and a molded keeper having a plurality of keeper teeth engageable with the plurality of teeth to inhibit movement of the keeper relative to the nut when the plurality of teeth engages the plurality of keeper teeth. The keeper has a radially inner side configured to engage a shaft to inhibit rotational movement of the nut relative to the shaft when the plurality of teeth engages the plurality of keeper teeth.

Abstract: A structure and method for a locking nut with a deformable member is provided. The locking nut has an elongated body relative to a comparable standard non-locking nut, allowing the nut to provide a standard length of thread for engaging bolt members while also defining a void for carrying the deformable locking member. The void has a forged side-wall structure that substantially engages the locking member within the void while shipping or handling the lock nut. The locking member deforms and flows into thread areas, thereby providing locking and vibration dampening functions, and also deforms or flows into the side-wall structures, thereby enabling the lock nut to impart sufficient frictional forces to the member to remove the deformed member from an assembly when the nut is removed. The locking forces imparted to the structure by the member may be varied and, therefore, increased by user-applied forces.

Abstract: A lock nut having a locking ring with a spoon-shaped lug. The lock ring includes a nut body having a bore with an interior threaded portion and a substantially cylindrical recess coaxial with the threaded portion of the bore. The recess includes a single notch on a portion of the recess. In addition, the lock ring includes a threaded locking ring positioned within the recess. The locking ring is deformed when threading the bolt onto the lock nut to frictionally grip the bolt. The locking ring also includes a single projecting lug at one side only of the locking ring, which fits into the notch to prevent relative rotation between the ring and the nut body. The lug includes a bowl-shaped nodule for collecting shavings gathering within the threads of the bolt and the interior bore of the lock nut.

Abstract: A bolt with a partially threaded shank has a plurality of locking grooves located on the shank between the thread and its head. The bolt is inserted through a component stack and spacing washers and a stepped reaction washer such that at least half of the locking grooves are left exposed. A deformable frusto-conical locking ring is positioned on a nut having a circular receiving cavity on one end. The nut and locking ring are positioned on the thread of the bolt and tightened so that the locking ring is deformed from a frusto-conical shape to a substantially flat disc such that its bore diameter is reduced, thereby retaining it within one of the locking grooves. The outer diameter of the receiving cavity abuts the stepped reaction washer.

Abstract: A method of sealing a bore, such as the threaded bore of a fastener, wherein the sealing element is preferably formed in place. The preferred sealing element is formed of a heat softenable plastically deformable material, such as a thermo-plastic resin, which is heated and deformed radially in the bore into a mechanical interlock with the bore inside the surface, such as thread. In the preferred method, a plunger or ram is driven into the sealing element which is supported on a die element in the bore. In the most preferred method, the ram simultaneously heats and deforms the sealing element, sealing the bore opening. The preferred female fastener element includes a generally tubular body portion having an axial bore which may be threaded adjacent one end. The sealing element seals the opening to the bore and the opposite end may be sealed with a disk spaced from the threads and forming a chamber.

Abstract: A structure and method for a locking nut with a deformable member is provided. The locking nut has an elongated body relative to a comparable standard non-locking nut, allowing the nut to provide a standard length of thread for engaging bolt members while also defining a void for carrying the deformable locking member. The void has a forged side-wall structure that substantially engages the locking member within the void while shipping or handling the lock nut. The locking member deforms and flows into thread areas, thereby providing locking and vibration dampening functions, and also deforms or flows into the side-wall structures, thereby enabling the lock nut to impart sufficient frictional forces to the member to remove the deformed member from an assembly when the nut is removed. The locking forces imparted to the structure by the member may be varied and, therefore, increased by user-applied forces.

Abstract: A structure and method for a locknut with a substantially rigid locking member is provided. The locking nut has an elongated body relative to a comparable standard, non-locking nut. The elongated body allows the nut to provide a standard length of thread for engaging bolt members, while also defining a void for the receipt and retention of a removable and replaceable rigid locking member. In a preferred embodiment, the member-carrying void has a forged gear-shaped side-wall structure that substantially engages the locking member within the void while shipping or handling the lock nut, and also causes the member to rotate with the nut as the nut is rotated onto a bolt member, and off of the bolt when loosened. One of either of the bolt threads and locking insert deform responsive to the compressive forces, locking the nut onto the bolt.

Abstract: An anti-loosening nail exclusively for wood includes an annular fix plate, a recess formed on an upper surface of the annular fix plate, and a hollow post extending down from the center section of the fix plate. The recess communicates with the center hole of the hollow post, and a washer is placed in the recess. When a screw is inserted in the center hole of the post, it screws with female threads formed in an upper portion of the center hole, and further engages with the washer to prevent the screw from loosen off of itself.

Abstract: A rod anchor is threadedly connected to a tension rod. The rod anchor includes an anchor head having a threaded first bore hole formed therein, and a sealing nut attached to the anchor head in sealing relationship therewith. The sealing member forms a second bore hole axially aligned with the first bore hole, whereby a threaded end of the tension rod extends through the second bore hole and into threaded engagement with the first bore hole. The sealing nut includes sealing material forming a seal between the sealing nut and the tension rod.

Abstract: A generally inverted “T” shaped, resiliently self locking, integral sportboard fastener is adapted to be received in a countersunk aperture formed in a sportboard such as a snowboard, ski, boogie board, skateboard or any other board which supports a person and has one or more structures attached thereto. The fastener comprises a noncircular base portion to be received within a countersink defined in the sportboard. The base and the countersink comprise two parallel sides and two opposite concentric arcs forming two opposite ends. A generally cylindrical integral ferrule portion extends upwardly from the base, through a bore defined in the sportboard, concentric with the countersink. The ferrule defines internal threads to receive a screw to secure a binding or other fixture to the sportboard. An internal annulus portion is defined at the juncture of the base and ferrule. A generally circular, preferably nylon, resilient insert ring is disposed within the annulus.

Abstract: A lock nut for engagement with a thread of a bolt, in which a thread block is arranged in the body thereof for engaging with the thread of the bolt and is made eccentric with respect to the axis of the nut body so that an initial tightening force of the nut on the bolt can be held for a long time.

Abstract: An improvement in the structure of a capped lock nut includes a nut body made of metal and formed with a shoulder extending upwardly from a top of the nut body and then inwardly to form a flange thereby providing an annular recess between the flange and an upper thread of internal threads of the nut body; a nylon packing ring snugly-fitted within the nut body; and a cap being a hemispherical shell member having an outer diameter which is just equal to an outer diameter of the shoulder of the nut body, whereby the cap can be easily welded to the nut body without causing damage to the nylon packing ring thus strengthening the engagement therebetween and increasing the production rate.

Abstract: A quick-operating locking fastener assembly for use in connecting members together, the fastener assembly comprising a fastener having a threaded shank, and a lock nut assembly receivable on the shank. The lock nut assembly includes a retainer having a passage for receiving the shank, and a seat formed in the retainer. An insert is held in the passage and has internal threads formed thereon for mating with threads of the shank. The insert is radially contractible and expandable between an engaged position in which the insert is threadably engaged with the shank and a disengaged position in which the insert is free to move axially along the shank without engagement of the insert with the shank.

Abstract: The bolt, in the one-way nut and bolt combination, includes a head, a stem, and bolt threads on said stem. A longitudinal channel is defined on the bolt stem by a plurality of notches extending through the crests of the threads. In one embodiment, each notch is defined by a radially aligned surface and an angularly displaced surface. The nut, in one embodiment, has a threaded bore that is complimentary to the bolt thread and includes at least one longitudinal cut-out. The nut further includes a compressible tine extending into the cut-out. The compressible tine has a body portion and a substantially radially aligned distal end portion. The distal end portion of the tine and the cut-out defines a narrow mouth leading to a wider throat deeper in the cut-out. The nut thread and the bolt thread cooperatively permit a user to translate the nut along the bolt threads by means of one-way rotation.

Abstract: There is provided a fastening device which includes a nut having a body. The body has a top face and a bottom face. The body further has an orifice extending therethrough. The system also includes a clamp-force indicating insert for use with the nut. The insert includes a portion extrudable across the top face of the nut. The nut further includes at least one insert-engaging portion.

Abstract: A fastening system comprising a bolt having a threaded shaft portion with a major thread diameter and a member having an aperture formed therein, said aperture being threaded over a portion thereof, a locking element having a preformed thread configuration being positioned within said aperture.

Abstract: A locknut which is durable and adapted to be used repeatedly is disclosed. The locknut has a body with a collar integrally extending from one end thereof for receiving a check washer. The check washer defines a polygonal hole therein. A periphery defining the polygonal hole is composed of a plurality of long edges and short beveled edges each arranged between two adjacent long edges. A length of each long edge is slightly smaller than an internal diameter of the body. By this arrangement, the extrusive portion of the long edges resulted from the thread of a bolt can be dispersed toward the short beveled edges to avoid a fracture of the check washer, thereby to maintain an effective elastic comeback of the check washer.

Abstract: A low profile double slot spanner locknut for engaging a threaded fastener having a substantially ring-shaped main body including a round outside edge, a hollow lower interior engagement portion and a hollow coined lip, portion. Two adjustment slots are positioned about 180.degree. apart on the outside edge and are used by a spanner drive tool for installing and adjusting the locknut. An impressionable nylon insert is positioned in a cavity in the coined lip portion. The insert is configured to further engage the thread of the fastener impressing the thread into the insert for self-locking during installation of the locknut.

Abstract: A sealing nut has an annular heat stabilized nylon sealing insert retained within a recess in a metallic nut body by a coined collar on the nut body. The sealing insert is initially formed symmetrical about a transverse median plane to enable bidirectional assembly into the nut body recess, and undergoes dynamic preloading when the collar is coined onto the periphery of the insert. When installed onto a threaded shaft extending from a bearing surface so that the coined collar is torqued against the bearing surface, the sealing insert forms a fluid-tight seal between the threaded shaft and a threaded bore in the bearing surface through which the threaded shaft extends. The nut body and sealing insert facilitate reduced manufacturing costs while enabling re-use without significant loss in sealing properties.

Abstract: A seal nut (10) provides a seal between a housing (14) having an opening (62) and a threaded member (60) having an axis (84) and a portion (196) received in the opening and a threaded portion (198) projecting from the housing. The seal nut includes a metal nut (72) and a deformable insert (74) movable with the nut. The nut has a main body portion (76) threaded on the threaded member. The nut has a plurality of circumferentially spaced tongues (92, 94, 98, 102) projecting axially from the main body portion and defining between them a plurality of slots (96, 100, 104, 106). The seal nut has a first position on the threaded member in which the nut (72) is spaced apart from the housing (14) and the tongues are undeformed.

Abstract: A fastener and method for fastening panels is disclosed. The fastener comprises a bolt and a nut with a locking feature to prevent loosening of the fastener from vibration after it has been set. The locking feature comprises a frustoconical tip on the inserted end of the bolt that engages a retainer ring in the nut. When setting the fastener, the retainer ring deforms around the outer end of the tip and slides down the narrowing frustoconical surface of the tip until the fastener is fully set. Unthreading of the bolt from the nut is prevented since the retainer ring will resist deformation along the increasingly larger diameter portions of the frustoconical tip. In another aspect of the invention, the nut is provided with shear tabs which engage a wrenching tool. These tabs are designed to shear when the fastener is fully set to prevent further application of torque by the tool.

Abstract: A plastic capped lock nut includes a metal body having a threaded bore extending axially between transverse opposite end faces and includes an annular wall extending outwardly of one of the end faces to define an open ended cavity for receiving a resilient lock ring mounted in the cavity in coaxial alignment with the threaded bore. An end cap of plastic material including an annular side wall and an outer end engages the lock ring and is sonically welded thereto. The annular wall of the metal body is deflected inwardly tightly against the lock ring to secure the ring in the cavity against rotation relative to the body. The end cap provides protection for exposed threads of a threaded rod or other element extending outwardly of the bore of the lock nut body and ring.

Abstract: A coupling for securing a handlebar to a bicycle frame, the coupling includes a compression nut and a bowl. An inner thread is formed in an upper end of the compression nut. A sealing ring has an outer thread formed on a lower end. The sealing ring is secured in place by a threaded engagement between the sealing ring and the compression nut when the handlebar standpipe is inserted through the sealing ring into the compression nut.

Abstract: A rod-shaped tension member formed of fiber reinforced composite material is utilized as an anchoring rod in foundation and mining construction, or as a reinforcing member in concrete and prestressed concrete construction. At least, in an axially extending region where it is to receive an anchoring member, such as a rod, the tension member has a continuous helical thread formed of alternating ribs and recesses. The anchoring member has a corresponding thread so that it can be screwed onto the tension member thread. An intermediate layer is provided between the threaded regions of the tension member and the anchoring nut, and is formed of a material affording large plastic deformation relative to the tension member when slight stress increases occur at overload conditions.

Abstract: A backward starting locknut comprises a polygonal-shaped metal nut having a threaded axial bore extending from a front end face normal thereto toward a recess formed in an opposite or backside of the nut body. A locking insert of resilient plastic material having a threaded bore aligned with that of the nut is seated in the recess and includes an annular, thick wall portion secured within the recess and an annular, thin wall portion integrally joined to the thick wall portion and extends outwardly from the recess and is provided with a threaded bore. The metal nut includes an annular wall section defining the recess and the wall section is deflected radially inwardly to compress the thick wall portion of the plastic insert and thereby constrict an inner portion of the threaded bore in order to establish a prevailing torque when a threaded rod is fully engaged in the bore of the insert.

Abstract: A lock nut comprising a lock member prepared from a shape memory alloy and serving as a backup member for a fastening nut.

Abstract: A blind fastener for installation in aircrafts or the like and method for forming same comprised of a threaded nut threaded on a threaded screw or stem member having a stem head with a deformable sleeve mounted on the stem member between the stem head and the threaded nut. A torque lock is created between the threaded nut and the stem member to provide torque of the nut against the threads of the stem member without damaging the threads of the nut and the stem member.

Abstract: An improved jewelry mounting construction for use in adapting pierced-ear earrings into earrings capable of being clamped on unpierced ears. Also disclosed is a construction for adapting pierced-ear earrings into stickpins. The improved construction comprises a clamping mechanism for securing a medium between opposed surfaces, one of those opposed surfaces being a receptacle for an earring post, with the receptacle having a means for securing the earring post of a pierced-ear earring therein. The mechanism for adapting pierced-ear earrings into stickpins comprises a post receptacle affixed to an elongated pin, with a means for securing an earring post therein.

Abstract: The invention relates to a bolt comprising a screw the threaded portion of which is provided with a guiding end, and a nut whose upper portion contains a self-locking washer with which is separably associated a ring internally concentric with the washer and ensuring the centering of the screw during its introduction into the nut.