This is an old case back press collet. It's made of sturdy aluminum. It can be used on both sides, such as for a 35.0mm case back with a 35.5mm collet. Sizes: 12 collets in 0.5mm increments from 24.0mm to 35.5mm 1 collet for 220/225mm 1 collet for 200/205mm 1 collet for 180/185mm 1 press collet... 16 pieces in total including the press. It's difficult to see in the image, but it has screw threads, so it can be attached to a general pressing tool.