ER Collet Range Chart

What it is

ER collets are slotted, spring-steel sleeves with an 8 degree half-angle taper. A nut pushes the collet into a matching chuck taper and the collet closes on the tool shank. ER collets are used in milling chucks, lathe tool holders and spindles. They grip over a small range of sizes, so one collet covers, for example, 9 to 10 mm.

The series number roughly matches the collet's outer diameter in millimeters.

How to identify

The collet is marked with its series and clamping range, such as "ER32 10-9" or "ER32 3/8." Measure the outside of the collet at its largest diameter to confirm the series if marks are worn.

Chart

Smallest sizes vary by maker. Check the collet maker's catalog for exact sizes, inch sizes and sealed (coolant-through) versions.

Key points

• Grip is best when the shank is at the upper end of a collet's range. A shank at the bottom of the range holds less well.
• Insert the shank at least two-thirds of the collet bore length.
• Snap the collet into the nut first, then thread the nut onto the chuck. A collet that is not snapped in will not release.
• Tighten to the chuck maker's nut torque with the right wrench. Overtightening damages the collet and nut.
• Precision collets (lower runout) are available and matter most for small tools.

Common mistakes

• Mixing ER series parts. An ER25 collet will not fit an ER32 nut or chuck.
• Clamping a shank smaller than the collet range.
• Running dirty collets and tapers, which raises runout and shortens tool life.
• Confusing ER collets with 5C, R8 or TG collets.

Governing standards: ISO 15488 (collets with 8 degree setting angle for tool shanks). Collet and chuck manufacturer's data.

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.