Tool, usually operated by hand, for tightening bolts and nuts. A wrench basically consists of a lever with a notch at one or both ends for gripping the bolt or nut so that it can be twisted by a pull at right angles to the axes of the lever and the bolt or nut. Open-end wrenches have ends with straight-sided slots that fit over the part being tightened; box-end wrenches have ends that enclose the nut and have six, eight, 12, or 16 points inside the head. A socket wrench is essentially a short pipe with a square or hexagonal hole and either a permanent or a removable handle.
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