The 8T is designed specifically for use with small burs and mandrels which do not exceed 1/4” [6.3mm] in diameter. The 8T is built to be a less expensive and semi-precise adjustable chuck for use on lathes with tapered shafts. This chuck opens with a CCW twist and closes with a CW twist. Unit Dimensions: 2 1/4” L x 1” Shank Diameter [6cm x 3cm]