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.

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.

The easiest way to determine what type of collet your machine has is to measure the length and diameter of the collet. All collets have a distinctive length and diameter. Use the chart below to determine the correct collet series for your machine.