This is a great set for any mill with R-8 spindle. The Collet chuck has the ER 20 easy change end and the R-8 shank with 7/16-20 drawbar threads. Once installed in the spindle you simply change out the collets on the end without that tedious loosening and tightening of the drawbar. The collet set is 7 pieces in the following sizes
1/8, 3/16, 1/4, 5/16, 3/8, 7/16, 1/2
Other er 20 collets sets are available as well- look for ST-161, ST-162 and ST-163
ER 20 collets are also available in metric sizes .