Nov. 11, 2026
Standard ER collets (DIN 6499 / ISO 15488) have a narrow elastic collapse range, normally **1 mm for most sizes. A collet stamped 12 mm nominally
clamps **11.0–12.0 mm** shanks. The key principle: **grip force, contact quality, concentricity and reliability are strongest near the nominal top end
and weaken as you move down toward the minimum of the range.
Mechanism
An ER collet works by being pulled axially into a 30° taper; axial nut torque converts to uniform radial squeeze around the shank. Its slotted, spring-steel body
has a limited elastic deformation window. When the shank is close to the collet’s marked size, the collet only needs a small amount of collapse. The contact
surface between collet bore and tool shank stays full, evenly distributed, and 360° continuous. That maximizes friction, torque transfer and rigidity.
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