The standard ER collet is the most widely used clamping system in the world. Made from Alloy spring steel and fully hardened these ER collets are ideal for many machining applications including boring, milling, reaming, tapping and grinding. MariTool offers ER collet sizes starting at ER8 through ER 40 .

Standards of ER Collets The numbers represent the opening diameter of the tapered receptacle in millimeters. As you tighten the nut on your holder, the ER collet collapses together to hold round tools or stock from 0.5-2 mm (or 0.0197-0.0787 in., depending on collet size) smaller than the collet internal diameter.

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.

The standard series are: ER-8, ER-11, ER-16, ER-20, ER-25, ER-32, ER-40, and ER-50. ER collets collapse to hold parts up to 1mm smaller than the nominal collet internal size in most of the series (up to 2mm smaller in ER-50, and 0.5mm in smaller sizes) and are available in 1mm or 0.5mm steps.