The ST 66 is a set of tools for using 5C collets in the Shopmaster Mill Turn machine. Due to the drawbar diameter, they will not work with earlier machines with the smaller spindle bore. The set consists of 2 5C collet blocks, 1 square for use with a 4 jaw chuck and 1 hex for use with the 3 jaw chuck. There is a drawbar that fits through the spindle to tighten the collets which has a knurled handwheel and a rotating sleeve so the drawbar can be loosened and tightened without friction against the end of the spindle. Contains 3 basic collets 1/4, 1/2, 3/4.