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.

However, the collet is most often used in routers to hold the cutting bits in place. The collet is secured to the tool using a hexagonal collet nut, allowing it to be tightened or loosened to the motor arbor.

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.

Collets have a life span of 400-600 hours, which roughly translates to between two and three months with the collet being used eight hours a day. When inspecting your collet, metallic damage, such as bell mouthing or burrs, should be checked with every tool change.