MT3 ER20 Collet Chuck Tool Holder Set 11 Pcs ER20 Collets Holder Taper: Morse Taper 3, MT3 Alloy steel and hardened to HRC 60-62. Tested T.I.R: 0.0001" Back Bar Thread :M12 x 1.75P 1 MT3 collets holder, 11Pcs ER 20collets, 1 wrench Collets Size (in inch): /8, 5/32, 3/16, 7/32, 1/4, 9/32, 5/16, 11/32, 3/8, 7/16, 1/2.