| 摘要 |
Coupling structure between screw head and tightening tool, constituted by a recess (3) with a curved concave surface on the free base of the head (1) of the screw (2) and by a protuberance (6) with a curved convex surface finishing the end of the tool (5). The recess has axial projections (4) internally and the protuberance (6) has meridional grooves (7). |
