Ultra Precision ER20 spring collet DIN 6499/B for clamping drill and tools with cylindrical shank. Resistant and practical for general use. The 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. They are ground both externally and internally then a superfinishing step is performed which guarantees an incredible surface finish of Rz 2.5.