This compact chuck is a good all-around workhorse for most lathe work. It has a clamping range of from 3/32" (2 mm) up to 1-3/16" (30 mm) diameter with the jaws in the normal position. With the jaws in the reversed position, work up to 2-1/4" (56 mm) can be gripped. The hole through the chuck is .687" (17 mm). Rotating the knurled ring closes all three jaws simultaneously to quickly grip round or hexagonal stock. Tommy bars (provided) are used in the holes in the side to tighten and loosen the chuck for more leverage.