These are known as the cutting, marking, and mortise. In principle they are alike, and consist of a sliding block which can be fastened at any part of a bar, near one end of which a small steel blade or point is fixed. The object of the marking gauge, the scriber of which is little more than a piece of sharpened wire, is to scribe straight lines parallel with the edge or end of a piece of wood. In the cutting gauge, the cutter, instead of being a mere point, is a thin flat blade, set across the stock, and adjustable to various depths. It marks a finer line than the marking gauge, and may, therefore, often be substituted for it with advantage. It is a very useful tool for cutting through thin wood instead of sawing it. A common form of both marking and cutting gauges is seen in Fig. 29.
The mortise gauge has two cutters, which are adjustable at various distances from each other and from the block. It is useful when two parallel lines have to be scribed, as when marking for the joint from which it takes its name; but it is possible to do without it and use one of the others. A mortise gauge is shown in Fig. 30.
Fig. 27. - Twist Bit and Gauge.
Fig. 29. - Marking Gauge.
Fig. 30. - Mortise Gauge.