Starrett - Knife-Style Marking Gauge No. 29B
Also called scratch gauges, Starrett’s marking gauges feature square cutters and adjusters. They were originally designed for scribing metal.
Marking, mortise, and combination gauges come in myriad styles and prices. What differentiates them from one another is the number and type of cutters each employs. Marking gauges have a single cutter for scribing one line at a time. Mortise gauges have two cutters and are used mostly for marking parallel lines to establish the width of a mortise. Combination gauges typically have three cutters: a single cutter on one side of the beam for use as a marking gauge and an additional pair on the other side of the beam for laying out mortises.
The Starrett scratch gauge has a hardened-steel fence, tempered-steel square blade, and a steel beam graduated in 64ths of an inch. This is an elegant tool, but the fence is the smallest of those tested, and the cutter had to be honed before it could be used. Given its size, the job wasn’t easy.