Correct option is D
A marking gauge and a mortise gauge are both layout tools used in woodworking and fitting work to mark lines parallel to a reference edge, but their primary difference lies in their construction and purpose. A marking gauge typically has only one scribing pin (spur). This single pin is used to draw a single line on the surface of the workpiece, which is useful for general marking tasks such as indicating cut lines or layout boundaries.
On the other hand, a mortise gauge is specifically designed for marking mortise and tenon joints, which require two parallel lines to define the width of the mortise. Therefore, a mortise gauge is equipped with two scribing pins. One pin is usually fixed, while the other is adjustable, allowing the user to set the exact width of the mortise according to the size of the chisel or tenon. This dual-pin arrangement enables precise and consistent marking of parallel lines, which is essential for accurate joint fitting.
Although both tools may appear similar in size, material, and even adjustment mechanism, these aspects are not their defining difference. The number of scribing pins is the most significant distinguishing feature because it directly relates to their function—single-line marking versus double-line marking.
