| 摘要 |
1484163 Woodscrews THERMA AG 8 Nov 1974 [9 Nov 1973] 48556/74 Heading F2H Two boards, e.g. of chipboard or plywood are secured together transversely of each other by a screw comprising a head 3, a plain cylindrical portion 2, and a thread-cutting portion 1 having at least one cutting helix 4 having an asymmetric profile with the rearward flank 5, i.e. the flank facing towards the head, substantially at right angles to the fastener longitudinal axis, the screw passing through a bore (11) (Fig. 2, not shown) through one board (9) so that its plain portion 2 bears therein, and the thread-cutting portion 1 being used to cut a thread in a blind hole (10) in the second board (8) parallel to the plane of the board, the thread being formed by removal of wood rather than deformation. The blind hole is predrilled to a diameter equal to the mean thread diameter of the screw. The screw may be of steel, zinc, light alloy, or hard plastics material, and it may have a multi-start thread 4, and may have longitudinal grooves along the thread-cutting portion. |
