Screw threaded fasteners

Abstract

A screw threaded insert to be installed in for example thermoplastic material by ultrasonic vibrations applied to the insert is double-ended and comprises a main helically ribbed portion separated from a minor portion formed with teeth or projections aligned with helical ribs, and a pilot portion. The pilot portion is to locate the insert in a performed bore in the required orientation of insertion, the toothed portion displaces material in complementary grooves, so as to facilitate travel of the insert into the material and ensure good filling of the inter-rib spaces.

I claim: 
     
       1. A double ended fastener which is symmetrical about a mid-point on its longitudinal axis, comprising: (a) a pilot portion at each end;   (b) an encircling groove next to each pilot portion;   (c) a minor toothed portion next to said groove .Iadd.and having helical teeth.Iaddend.;   (d) a second like groove next to said minor toothed portion; and   (e) a major toothed portion next to said second groove and extending towards said mid-point, .Iadd.said major toothed portion having helical teeth, .Iaddend.the fastener having a female screw-threaded bore provided over the whole of its length.   
     
     
       2. A fastener as claimed in claim 1 wherein a pair of major toothed portions are provided which are symmetrically located with respect to said mid-point, and are separated by a peripheral encircling groove. 
     
     
       3. A fastener as claimed in claim 2 wherein said major toothed portions are helically ribbed in opposite directions of helix angle. 
     
     
       4. A fastener as claimed in claim 2 wherein the encircling groove at the mid-point has a diameter which is substantially the same as a diameter of the encircling groove between the major toothed portion and the minor toothed portion. 
     
     
       5. A fastener as claimed in claim 1 wherein each minor toothed portion is frusto-conical with the minor dimension of the frusto-cone located towards the adjacent end of the fastener and the major dimension adjacent said major toothed portion. 
     
     
       6. A fastener as claimed in claim 1 wherein each pilot portion is frusto-conical with the minor dimension of the frusto-cone located at the extreme end of the fastener and the major dimension adjacent said minor toothed portion. 
     
     
       7. A fastener as claimed in claim 6 wherein the minor dimension of each pilot portion greater than the diameter of the adjacent encircling groove and the diameter of the latter is substantially equal to the minor dimension of the frusto-conical minor toothed portion. 
     
     
       8. A double-ended fastener which is symmetrical about a midpoint on its longitudinal axis, comprising: (a) a pilot portion at each end;   (b) an encircling groove next to each pilot portion;   (c) a minor toothed portion next to said groove;   (d) a second like groove next to said minor toothed portion; and   (e) a pair of major toothed portions which are symmetrically located with respect to said midpoint and are separated by a peripheral encircling groove, wherein the encircling groove at the midpoint has a diameter which is substantially the same as the diameter of the encircling groove between the major toothed portion and the minor toothed portion. .[.   
     
     
       9.  A double-ended fastener which is symmetrical in profile about a midpoint on its longitudinal axis, the fastener comprising: (a) a pilot portion at each end;   (b) an encircling groove next to each pilot portion;   (c) a minor toothed portion next to each encircling groove;   (d) a second like groove next to each minor toothed portion; and   (e) a major toothed portion extending between the second grooves and symmetrical in profile about the midpoint, the fastener having a female screw-threaded bore provided over the whole of its length..].  .[.   
     
     
       10.  A fastener as claimed in claim 9 wherein said major toothed portion is helically ribbed..].  .Iadd. 
     
     
       11.  A double ended fastener which is symmetrical in profile about a midpoint on its longitudinal axis, said fastener comprising: (a) a pilot portion at each end of said fastener;   (b) an encircling groove next to each of said pilot portions;   (c) a minor toothed portion next to each of said grooves, each of said minor toothed portions having helical teeth;   (d) a second encircling groove next to each of said minor toothed portions;   (e) a major toothed portion between said second grooves, said major toothed portion having helical teeth, the helix of the teeth of each of said minor toothed portions extending in the same direction as the helix of the teeth of the adjacent major toothed portion and the teeth of each of said minor toothed portions being helically aligned with the teeth of the adjacent major toothed portion; and   (f) an internal screw-threaded bore extending over the whole of the length of said fastener..Iaddend. .Iadd.12. A double-ended fastener which is symmetrical about a midpoint on its longitudinal axis; said fastener comprising:   (a) a pilot portion at each end of said fastener;   (b) an encircling groove next to each of said pilot portions;   (c) a minor toothed portion next to each of said grooves, each of said minor toothed portions having helical teeth;   (d) a second encircling groove next to each of said minor toothed portions;   (e) a pair of major toothed portions provided between said second grooves and separated by another encircling groove, each of said major toothed portions having helical teeth; and   (f) an internal screw-threaded bore extending over the whole of the length of said fastener..Iaddend. .Iadd.13. A double-ended fastener which is symmetrical about a midpoint on its longitudinal axis, said fastener comprising:   (a) a pilot portion at each end of said fastener;   (b) an encircling groove next to each of said pilot portions;   (c) a minor toothed portion next to each of said grooves, each of said minor toothed portions having helical teeth;   (d) a second encircling groove next to each of said minor toothed portions;   (e) a pair of major toothed portions provided between said second grooves and separated by another encircling groove, each of said major toothed portions having helical teeth, the helix of the teeth of the major toothed portions extending in opposite directions, the helix of the teeth of each minor toothed portion extending in the same direction as the helix of the teeth of the respective adjacent major toothed portion, and the teeth of each minor toothed portion being helically aligned with the teeth of the respective adjacent major toothed portion; and   (f) an internal screw-threaded bore extending between the ends of said fastener. .Iaddend.