Marking gauges consist of two main parts, a fence and a stem. The stem carries a pointed metal spur at the end. The fence can be fixed to any position along the stem by a wedge. Marking gauge is an essential tool for basic carpentry and joinery. It is used to score a single line parallel to the face side or face edge, when planning a piece of timber to size, and for marking out rabates and simple joints. The spur is simply a nail with its head cut off and  hammered into the end of the stem.
 

To use the gauge first set the distance from the spur to the fence. Tighten the fence to the stem by tapping the back of the wedge with a piece of wood. Check the setting and make final adjustments by tapping either end of the stemon the bench top. To loosen the fence tap the front of the wedge.