| 摘要 |
The screw head has a non-circular internal space for a correspondingly shaped screw driver. The space (4) is shaped as a regular symmetrical polygon, but is not triangular, square, or hexagonal. The outer contour of a screw driver fitting a certain screw is outside the fit of neighboring inner circles of a screw series. The outer contour of a randomly used screw driver does not fit the inner circles of each screw in a series. The internal space is a symmetrical polygon with alternating large (5) and curved small (6) surfaces. The space may be a pentagon, with cut corners, resulting in five large and five small surfaces. A projection (10) inside the space extends almost to the outer surface (11) of the screw head (3).
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