0.00031 at collet face. Rear thread for pull stud is 1 - 8. Works on all CAT 50 machines.All critical tool holder surfaces precision ground. Made from alloy structural steel hardened to HRC48 - 52 for long, durable service life. Taper ground to high precision AT3 accuracy. Collet Chuck accepts all ER20 collets. 12.7 × 5.4 × 5.4 in.