General Tools 18 Round Head Protractor is an essential tool for students, machinists, carpenters and woodworking hobbyists. Constructed of durable stainless steel, the protractor with its 6" adjustable arm is ideal for setting bevels, taking measurements and transferring angles. This round head protractor has a 0 to 180° semi-circle scale in forward and reverses directions to measure all angles. Measure an angle with the small stainless steel arm which glides smoothly for precise alignment. Use the knurled thumb nut to lock the arm into place as you take measurements. Its stainless steel construction gives it strength, durability and the ability to resist rust.