| 摘要 |
A screw is disclosed to have a compound recess in the head thereof, which compound recess having a center square portion, four symmetrical fan-shaped portions in contact with the four angles of the center square portion, and a narrow elongated slot portion extending across two opposite angles of the center square portion. The ratio between the depth of the narrow elongated slot portion and the depth of four angles of the center square portion is within 2/3:1.
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