Kaufhof APM-1277 Round Head Protractor Cum Depth Gauge Made from polished stainless steel Narrow 150 mm / 6 Inch rule graduated 64 on one side and 0.5 mm at reverse Graduated from 0  180 Blade Length: 150 mm 6 inches, Graduations: 0.5 mm or 64ths inches Spring tension nut to secure rule to desired depth and angle