| 摘要 |
654,422. Self-tapping screws. BERMAN, B. Z., and BERMAN, J. R., (trading as BERMACK CO.). March 5, 1948, No. 6921. Convention date, March 5, 1947. [Class 83 (iii)] A self-tapping screw comprises a head 1, Fig. 1, a threaded body 2, a threaded reduced end portion 3, a plurality of grooves equally-spaced around its periphery, each groove 7 being asymmetrical in relation to any radius passing through it and one face of each groove forming a cutting edge with the peripheral surface of the screw, said face being a planar surface forming a cutting angle B, Fig. 2, of not more than 90 degrees, another face of each groove forming, with the periphery of the screw, an angle of more than 90 degrees, each groove extending into the screw in the radial sense deeper than the minor diameter of the screw, whereby the groove constitutes a substantial chip reservoir located in the reduced end portion. Screws with two, three, and four cutting edges equally spaced around the periphery are described. The cutting edges may be formed by cutting slits 10, Fig. 9, in the screw and the slits may also be of stepped formation. |
