The 2278 Insize combination set for inside, outside and angular measurements. Made of stainless steel for longer tool life and durability from machine shop wear. Center head: To locate center of round workpieces, Accuracy: 0.15mm. Protractor head: To set the blade at desired angle to an edge of a workpiece, and can be used to measure angles Range: 0-180 Degree, Accuracy: 7min. Square head: To set the blade at 90 Degree or 45 Degree to an edge of a workpiece, Accuracy: 8min for 90 Degree square, 10min for 45 Degree square. Blade: Range: 300mm/12", Graduation: 0.5mm and 1/32" on front face, 1mm and1/64" on back face. Optional accessory: rigid rule (code 7113) .