The mortise marking gauge has one side of the stem with two pins, one fixed and one that can be adjusted using the spur locking screw. The pins are made a set distance apart so that they match the intended mortise size.
Mortise gauge pin
The mortise gauge also has a single spur on the opposite side of the stem which works like a regular marking gauge. This is why the mortise gauge is also known as a combination gauge as it can do a combination of wood working tasks.
Mortise gauge fence
The mortise gauge has a fence, the same as other marking out gauges, used to set the measurement from the edge of the workpiece.
Fence locking screw on a mortise gauge
Once the fence of the mortise gauge is in position, it is locked in place by turning the fence locking screw clockwise. The fence locking screw is usually on the top of the fence, but can be on the side of the fence on some models.
Spur locking screw on a mortise gauge
The mortise gauge’s adjustable pin / spur is controlled by the spur locking screw. This is located around the back end of the stem. The screw is pulled backwards and forwards to move the pin into the required position and then turned clockwise to lock it in place.
Mortise gauge stem
As with all marking out gauges, the main body is known as the stem. This is a solid piece of wood that connects all the parts, and on the mortise marking gauge it holds the adjustable pin and locking screw. The screw pulls a piece of wood within the stem to control the adjustable pin.