| 摘要 |
An enclosed wrench has a drive head defined at an end provided with an opening therein, on the internal surface of the opening a plurality of uniform drive protrusions being disposed respectively and each of which is isosceles triangle structure, the sidelines of each adjacent pair of drive protrusion are crossed. A vertex of each drive protrusion is identical with that of a vertex of the respective isosceles triangle. The height of the isosceles triangle is equal to the sum of the absolute value of the international tolerance of the wrench and that of the corresponding working piece to be driven.
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