ER16 series collets have a capacity of .015-.4375 inches. Each ER16 collet has a range of .039 inches(1mm). ER16 Collets .118 and smaller have a range of only .015 inches. The size indicated on the collet is the largest size it can hold and can be collapsed smaller within its collapse range mentioned above. For example, ER16-1/4 can grab a round shank from .250 diameter to .211 diameter. Please refer to our ER16 Collet print for general ER16 dimensions.