| 摘要 |
789,272. Screw - heads. AMERICAN SCREW CO. March 15, 1956 [March 16, 1955], No. 8204/56. Class 89(2) A screw has a tool-receiving recess 11 in its end 10 extending along its longitudinal axis, and comprising a central portion 12 and grooves 13 extending outwardly from the portion with their substantiallyvertical medial-planes parallel to but spaced from true radial-planes. The driving-wall 15 of each groove lies closer to the true radial-plane than does the other wall 16, and in one arrangement, is coincident with said plane. Adjacent walls 15, 16 of adjacent grooves are joined together by surfaces 17, 18 of the central-portion. In modifications, the surfaces 17, 18 are replaced by single oblique or curved surfaces. The bottom-wall of the central-portion is conical and may extend into a shallow cylindrical recess. The bottomwalls of the grooves extend upwardly to meet the screw-end at the periphery of the grooves.
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