A pocket sized stainless steel gauge that's 5 tools in 1: a bevel protractor for measuring and laying out angles, a center finder, a circle divider (up to 9 equal parts), a drill point gauge for checking 590 angle drill points, and a tap and drill table that shows popular tap sizes with correct drill sizes (national thread only). The 4" rule has etched graduations in 64ths and millimeters.