ER collets, designed by Rego-Fix in the 1970s, are among the most widely used and popular collets in the world, and today are available from multiple producers. They offer a wide clamping/collapse range and high accuracy, and while they are designed for tool holding they can be used to secure workpieces on small lathes/machines as well. The number in the name designates the size of the collet’s opening, so for an ER40 collet, that size is 40mm (technically 41mm, with a clamping range between 3 and 26mm.)