Measure, Mark And Scribe Trim Lines On Sheet Metal In One Easy Operation. Set Desired Trim Depth On The 1/8" (3.2 Mm) Graduated Scriber Extension And Tighten Knob. The Use Of A Common Sheet Metal Screw Makes Point Replacement Practical And Economical. Pocket Size Tool Is Constructed Of Rust Resistant Nickel Plated Steel. Knob Assembly With Hardened Steel Bolt Insert Will Not Strip Out.