A marking gauge is a device for marking a cutting line on wood or other materials. The gauge consists of a beam and a fence, through which the beam passes. The fence may be fixed to the beam by a set screw or a wedge. The beam has a scratch pin or other marker set near one end of the beam. The fence is set so that the distance from the inner surface of the fence to the scratch pin equals the desired width of the board or panel. The fence is held against the edge of the wood, and the marking gauge is pushed along the wood, leaving a scratch mark to guide the cut.
This 6 inch long mortise gauge is made from rosewood and brass. It has a fixed scratch pin near the end of the beam, and a movable scratch pin between the fixed pin and the fence. The movable scratch pin is adjusted by turning the thumb screw at the far end of the beam. The fence is held in a desired position by the screw on top of the fence.