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The marking gauge is designed to help you make accurate
lines parallel to the edge of a panel or board. A common wood gauge is about 8
inches long, with a scribing spur close to one end. A sliding head may be moved
through the body and clamped using a thumbscrew at any place. When choosing a
gauge, get one made from hardwood secured with a brass or metal head. A special
double-bar gauge with two spurs is designed for marking off a mortise. The
gauge is set once, and the spur on each side is used in turn to show the
mortise area.
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