Auxilliary Circular Carbide Scriber Collet Adapter for Cat. 827 need for collet changes on Bridgeports and similar machines. It can also be used with any other attachment with a 3/8" post. The progressive steps are: 1/4", 5/16", 3/8", 1/2", 5/8", 3/4" and 1". Step depths vary from .100" to .200".