Mortise Gauge

A mortise gauge, also called a mortice gauge, is a woodworking tool used by a carpenter or joiner to scribe mortise and tenon joints on wood before cutting, commonly made of hardwood with brass fittings. Like a simpler marking gauge it has a locking thumb screw slide for adjusting the distance of the scribe from the edge of the wood, but it carries two protruding pins, called spurs, that scribe both sides of a mortise at the same time. One pin is fixed to the body and the other rides on a sliding fence, so mortises of different widths can be marked. Some mortise gauges have a retractable spur so they can also serve as a marking gauge, though many carpenters keep the two tools separate since a mortise gauge is a more expensive, higher precision instrument. On double-beam designs the gauge can be wrapped around a tool such as a chisel for extra accuracy on complex joints.