ER25 series collets have a capacity of 1mm-17mm. Each ER25 collet has a range of (1 mm). The size indicated on the collet is the largest size it can hold and can be collapsed smaller within its collapse range of (0.9mm). For example, ER25-3mm can grab a round shank from 3mm diameter to 2.1mm diameter.

Collets are used to hold a tool in a central position as it rotates. As the tool is inserted into the collet, the device expands and provides uniform pressure that holds the tool in place. However, if the collet stretches too far, it cannot secure the instrument properly and may lose shape.