| 摘要 |
626,729. Self-tapping screws. AMERICAN SCREW CO. Dec. 9, 1946, No. 36347. Convention date, Dec. 7, 1945. [Classes 83 (ii) and 83 (iii)] A method of making a self-tapping screw comprises first rolling helical grooves 5 of relatively high pitch on to the shank, and then rolling an interrupted screw thread 6 of relatively low pitch. Each interrupted portion 7 of the screw thread has at its leading end a cutting edge 8 which is inclined rearwardly from bottom to top, relative to the direction of rotation of the screw. Specifications 491,680 and 491,710 are referred to. |
