| 摘要 |
798,657. Self-tapping screws. GENERAL AMERICAN TRANSPORTATION CORPORATION. June 6, 1956 [April 30, 1956], No. 17545/56. Class 83 (3). A self-tapping screw comprises a number of longitudinal flutes 6 in the tapping-section 5 providing cutting-edges 8 on the interrupted threads, each flute terminating between a pair of adjacent thread-convolutions and at threadroot level. The flutes, preferably of substantially constant depth and terminating between the same or different pairs of thread-convolutions, are formed in a thread-rolling and flute-producing operation, performed by a pair of dies. The faces 8, 9 formed by the flutes may converge towards the bases of the flutes. Specification 491,710 is referred to. |
