Measure, mark and scribe trim lines on sheet metal in one easy operation. Set desired trim depth on scriber extension and tighten knob. The stop at the end of the scriber sleeve glides along edge of work as a 6 x 3/8 sheet metal screw point scribes a clean, hard line. Adjustable from 1/4 inch to 12-1/2 inches (6.4 to 318 mm) depths in 1/8″ (3.2 mm) graduations. Rotate the scriber extension and knob end to end for depths larger than 6-1/2?(165 mm). The use of a Zip-In sheet metal screw makes point replacement practical and economical. Scrow point is protected when tool is closed. Pocket size tool is constructed of rust resistant nickel plated steel. Knob assembly with hardened steel bolt insert will not strip out.