| 摘要 |
A screwdriver bit has a pair of opposite driving faces which taper toward each other at its bit end which faces are arcuate in form, concave-out and terminate in a bit edge which is double concave in cross section, thicker at both its ends than at its center. The center thickness is made small enough to enter the slot of small screws, and the end thicknesses are great enough that the center of the bit edge does not make contact with the slot of larger screws. A single bit can drive and remove screws of a wide range of sizes.
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