The General Tools Square Head Steel Protractor is preferred by machinists, draftspeople and mechanics for setting bevels and measuring and transferring angles. Made of ground stainless steel for optimum accuracy. Permanently etched graduations from 0 to 180° in opposite directions. Adjustable protractor arm locks into desired position with knurled thumb nut. Length of adjustable protractor arm: 6 in. Head dimensions: 3-3/8 x 2 in.