These collets are usually found in a standard series as: ER-8, ER-11, ER-16, ER-20, ER-25, ER-32, ER-40, and ER-50. The numbers represent the opening diameter of the tapered receptacle in millimeters.

ER16 Collets- ER16 Standard Collets Our ER16 collets have a capacity ranging from . 0625 - . 4062 inches or in metric sizes from 1mm up to 10mm. The number shown on the collet is the largest size that particular collet can hold, but it can be tightened to a smaller size.