ER collet sizes: ER11 to ER40 clamping ranges
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ER is the most widely used collet system and is standardised as DIN 6499. The number after ER is the size of the collet series. A bigger ER number means a bigger collet, nut and chuck, and a wider range of tool shank sizes.
How the range works
Each collet is sold by its nominal size in mm. That size is the largest shank it holds. An ER collet closes by about 1 mm, so it clamps shanks from 1 mm under the nominal size up to the nominal size.
Example: a 10 mm ER collet holds shanks from 9 mm to 10 mm. A 9.5 mm shank also fits that collet.
The small ER8 and ER11 series close by only about 0.5 mm.
Collet sizes in our listings
| Series | Collet sizes we list | Steps |
|---|---|---|
| ER16 | 1 to 10 mm | 1 mm |
| ER20 | 1 to 10 mm | 1 mm |
| ER25 | 1 to 15 mm | 1 mm |
| ER32 | 1 to 20 mm | 1 mm |
| ER40 | 3 to 25 mm | 1 mm |
This table shows the sizes we list, not the full range of each series. Under the standard, the larger collets go further: up to 13 mm for ER20, 16 mm for ER25 and 26 mm for ER40.
We also sell ER11 collet chucks, but we do not list ER11 collets at present.
Which should I buy?
- Match the series to the chuck. An ER32 collet only fits an ER32 chuck and nut.
- Match the size to the shank. Measure the shank with a micrometer or caliper and pick the collet whose range includes it.
- Stay inside the range. A shank smaller than the collet's 1 mm range needs a smaller collet.
- Smaller series for small tools, larger for big ones. Pick the series from the largest shank you will hold.
Collets wear, so replace any that are damaged or loose on the shank.