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.

Your first consideration should be the size of end mills or drills you will be using most often. If you are doing smaller work you would require smaller diameter range collets. Generally you may prefer the ER16 and ER32 sizes. ​If you are doing very small work then perhaps an ER11 set would be the best choice.

ER collets are the most widely used clamping system. The standard series are: ER-8, ER-11, ER-16, ER-20, ER-25, ER-32, ER-40, and ER-50.

Collets form a collar around a workpiece or tool. Generally manufactured from spring steel or other similar materials, they are usually made with a vertical kerf, a slit created by cutting a piece of material with a saw. Collets are used to hold a tool in a central position as it rotates.