An R8 collet is a specialized clamping device used in machining and milling. It is designed to hold workpieces securely in place, allowing for precise cutting, shaping, and drilling operations. The “R8” designation refers to the taper size of the collet, which is commonly found on milling machines.

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.

ER collets have a wide clamping range and high accuracy. While they are designed for tool holding, they work great for work holding in small lathes. With a full set of ER collets you can hold any diameter that is in the clamping range of the set. There are several types of collets that look like ER collets.

Collets Vs Jaw Chucks. Collets and chucks are two common types of mechanism used to hold spindle tooling or workpieces. Technically speaking, a collet is a type of chuck, but the two terms are usually used exclusively. A 'chuck' usually refers to any type of work holder which is not a collet.