| 摘要 |
997,716. Screws, covers for and prevention of their overtightening; bolting. ILLINOIS TOOL WORKS Inc. July 17, 1962, No. 27444/62. Heading F2H. [Also in Division B3] The clamping surface 26 of the head of a screw, e.g. for securing wallboard 11 to a support 12, flares outwardly from the shank to a greater degree nearer the periphery 25 of the head than it does near the shank. The generatrix of the flaring surface may have a single radius of curvature, Fig. 5 (not shown), or the surface may have a circular line as in Fig. 6, where lines or curves meet. The head has a "Phillips" (Trade Mark) recess and the screw is self-tapping by virtue of a slot 22 in the shank. The screw is screwed home until the head face 24 is just below the wallboard face level (there may be a shoulder-forming portion 35, Fig. 6, to prevent overtightening) and the head recess and the face 24 receive a cement, Fig. 2 (not shown), to conceal the screw. The surface of the support 12, where it receives the wallboard 11 may be roughened to prevent skidding of the screw-point on insertion. |
