| 摘要 |
1312137 Self-tapping screws KEYSTONE CONSOLIDATED INDUSTRIES Inc 14 Sept 1970 43839/70 Heading B3N A thread-forming screw comprises a body portion 18 and a tapered end 19, a continuous thread 21 runs the length of the screw; in cross-section the screw has 5 flats and 5 rounded corners or lobes whereby the flats form relief portions, the screw thread is of full depth at the corners and of reduced height along the flats to produce concave crests; on the tapered end both the lobes and the flats have concave crests which increase in concavity as the free end of the screw is reached. The screw is formed from a blank having flats 16 and lobes 15, the thread being rolled on to the screw in a conventional manner. The length of the tapered end is equal to the pitch of 2 or 3 threads. |
