ER collets
ER collets (DIN 6499 / ISO 15488)
| Series | Collet OD mm | Length mm | Standard nut thread | Clamping range mm | Each collet grips (mm) |
|---|---|---|---|---|---|
| ER8 | 8.5 | 13.5 | - | 0.5 - 5 | 0.5 |
| ER11 | 11.5 | 18 | M14 × 0.75 | 0.5 - 7 | 0.5 |
| ER16 | 17 | 27.5 | M22 × 1.5 | 0.5 - 10 | 1 |
| ER20 | 21 | 31.5 | M25 × 1.5 | 1 - 13 | 1 |
| ER25 | 26 | 34 | M32 × 1.5 | 1 - 16 | 1 |
| ER32 | 33 | 40 | M40 × 1.5 | 2 - 20 | 1 |
| ER40 | 41 | 46 | M50 × 1.5 | 3 - 26 | 1 |
| ER50 | 52 | 60 | varies by maker | 5 - 34 | 2 |
Each ER collet closes down from its marked size by its grip range: an ER32 collet marked 12 holds 11 – 12 mm. To hold a size exactly on the boundary, use the collet marked at or just above it (for 12 mm use the 12 collet, not the 13). Always click the collet into the nut before screwing the nut onto the holder, and never tighten an empty collet.
Which ER series fits my shank?
| Shank | ER series that will hold it |
|---|---|
| 1 mm | ER8, ER11, ER16, ER20, ER25 |
| 2 mm | ER8, ER11, ER16, ER20, ER25, ER32 |
| 3 mm | ER8, ER11, ER16, ER20, ER25, ER32, ER40 |
| 3.175 mm (1/8") | ER8, ER11, ER16, ER20, ER25, ER32, ER40 |
| 4 mm | ER8, ER11, ER16, ER20, ER25, ER32, ER40 |
| 5 mm | ER8, ER11, ER16, ER20, ER25, ER32, ER40, ER50 |
| 6 mm | ER11, ER16, ER20, ER25, ER32, ER40, ER50 |
| 6.35 mm (1/4") | ER11, ER16, ER20, ER25, ER32, ER40, ER50 |
| 8 mm | ER16, ER20, ER25, ER32, ER40, ER50 |
| 9.525 mm (3/8") | ER16, ER20, ER25, ER32, ER40, ER50 |
| 10 mm | ER16, ER20, ER25, ER32, ER40, ER50 |
| 12 mm | ER20, ER25, ER32, ER40, ER50 |
| 12.7 mm (1/2") | ER20, ER25, ER32, ER40, ER50 |
| 16 mm | ER25, ER32, ER40, ER50 |
| 19.05 mm (3/4") | ER32, ER40, ER50 |
| 20 mm | ER32, ER40, ER50 |
| 25 mm | ER40, ER50 |
| 25.4 mm (1") | ER40, ER50 |
| 32 mm | ER50 |
Tips
- The series number is roughly the collet's outside diameter in mm.
- Collet capacity is the largest size; full sets step in 1 mm (0.5 mm for ER8/ER11, 2 mm for ER50).
- Clean the taper, collet and nut before fitting. Grit causes run-out and marks the bore.
- Hold the cutter shank for at least two-thirds of the collet length.
- Tighten with the correct spanner. Over-tightening does not improve grip and damages the nut.
- Imperial shanks (1/4", 1/2") fit the metric collet whose range covers them, e.g. 6.35 mm in a 7 mm collet.
Other collet systems
Other common collet systems
| Type | Used on | Capacity | How it is held |
|---|---|---|---|
| 5C | Lathe spindles, indexers, collet blocks | Up to 1-1/16" round | Pulled in by a draw tube (external thread on collet) |
| R8 | Bridgeport-type milling machines | Commonly to 3/4" | 7/16"-20 UNF drawbar; keyed body |
| MT2 / MT3 collets | Small mills and lathes with Morse spindles | To about 1/2" (MT2) / 5/8" (MT3) | Drawbar thread depends on the machine - check before buying |
| Screwed-shank (Clarkson/Autolock type) | Milling chucks for threaded-shank cutters | Cutter shank sizes | Collet bore is threaded to suit the cutter's screwed shank; plain shanks need an ER or side-lock holder |