13pcs Precision R8 Collets Set 1/8 - 7/8" Mill Chuck Holder for Bridgeport .0006 Size: 1/8" 3/16" 1/4" 5/16" 3/8" 7/16" 1/2" 9/16" 5/8" 11/16" 3/4" 13/16" 7/8" Accuracy .0006" TIR Drawbar Thread: 7/16"-20 Precision ground to close tolerance Hardened and ground throughout