Protractor arm (blade) is 6 inches long; head is 3-3/8 inches wide by 2 inches high. Permanently etched graduations from 0 to 180 degrees in opposite directions Used by machinists, draftsmen, mechanics, and engineers for setting bevels and transferring angles 180° Max Measurement, 1° Dial Graduation, Accuracy Up to 30 Minutes, 0 to 90 to 0 Dial Range. SPI 30-393-3 Rectangular head protractor with 6 inch blade. 180° Max Measurement, 1° Dial Graduation, Accuracy Up to 30 Minutes, 0 to 90 to 0 Dial Range. Used by machinists, draftsmen, mechanics, and engineers for setting bevels and transferring angles. Permanently etched graduations from 0 to 180 degrees in opposite directions. Protractor arm (blade) is 6 inches long; head is 3-3/8 inches wide by 2 inches high.