The standard series are: ER-8, ER-11, ER-16, ER-20, ER-25, ER-32, ER-40, and ER-50. The "ER" name came from an existing "E" collet (which were a letter series of names) which Rego-Fix modified and appended "R" for "Rego-Fix". The series number is the opening diameter of the tapered receptacle, in millimetres.

Standards of ER Collets 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.

Each ER32 collet has a range of . 039 inches(1mm).

The standard series are: ER-8, ER-11, ER-16, ER-20, ER-25, ER-32, ER-40, and ER-50. ER collets collapse to hold parts up to 1mm smaller than the nominal collet internal size in most of the series (up to 2mm smaller in ER-50, and 0.5mm in smaller sizes) and are available in 1mm or 0.5mm steps.