Guide · Collets and collet nuts
ER11 vs ER16 vs ER20: which shanks each collet system holds
The ER number names the collet size, not the shank. Maker ranges for ER11, ER16 and ER20, and which systems hold 1/4, 3/8 and 1/2 inch bits.
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Short answer
The number after "ER" names the collet size, not the bit it holds: an ER11 collet does not take an 11 mm shank.[1] Your spindle or router nose decides the system. Then the bit's shank decides which collet in that system you need. In the catalogs checked, ER11 stops at about 1/4 inch, ER16 at 10 mm or 3/8 inch, and ER20 at 13 mm or 1/2 inch.
Start with the spindle, not the bit
You cannot pick a collet system on its own. The spindle nose has a taper and a thread made for one ER series, so an ER20 collet will not go into an ER11 spindle. Check the spindle or router maker's documentation for its series first.
Once you know the series, match the collet to the shank. An ER11 collet does not hold an 11 mm shank; the ER11 catalogs checked all stop at 7.0 mm, about 1/4 inch.[1]
What each system holds, by maker
Collet makers publish their own ranges, and they do not all agree at the edges.
- ER11: Galaxy, Command Tool and Somma all top out at 7.0 mm, and Command Tool and Somma top out at 1/4 inch.[1] Somma lists ER11 at 1/16-1/4 inch and 1-7 mm.[2]
- ER16: Galaxy's ER16 ranges run up to 9.0-10.0 mm.[3] Command Tool's metric ER16 collets also stop at 9.0-10.0 mm, and its largest inch ER16 collet clamps 0.336-0.375 inch.[4] Somma lists its English ER16 range up to 13/32 inch.[2]
- ER20: Galaxy's largest ER20 range is 12.0-13.0 mm.[5] Command Tool's ER20-F500 clamps 0.461-0.500 inch, and its largest metric ER20 collet clamps 12.0-13.0 mm.[6] Somma lists ER20 at 1/16-1/2 inch and 1-13 mm.[2]
| System | Largest size listed (Galaxy / Command Tool / Somma) | 1/4 in | 3/8 in | 1/2 in |
|---|---|---|---|---|
| ER11 | 7.0 mm / 7.0 mm and 0.250 in / 7 mm and 1/4 in | Yes, top of range | No | No |
| ER16 | 10 mm / 10 mm and 0.375 in / 10 mm and 13/32 in | Yes | Yes | No |
| ER20 | 13 mm / 13 mm and 0.500 in / 13 mm and 1/2 in | Yes | Yes | Yes |
A 1/2 inch shank sits outside every ER16 range checked: Galaxy and Command Tool stop at 10 mm, and Somma's 13/32 inch is about 10.3 mm.[4] For 1/2 inch bits you need ER20 or larger.
Inch shanks in millimeters
Inch and metric sizes are close enough to confuse, and the difference matters. The exact figures:[7]
| Shank | Exact size |
|---|---|
| 1/8 in | 3.175 mm |
| 1/4 in | 6.35 mm (0.35 mm larger than 6 mm) |
| 3/8 in | 9.525 mm |
| 1/2 in | 12.7 mm |
A 1/4 inch shank will not go properly into a 6 mm collet. REGO-FIX advises never clamping a shank larger than the collet's nominal size and using the next larger collet instead.[8] Buy the 1/4 inch collet for 1/4 inch bits.
One collet per shank size
An ER collet only closes a little. PreciseBits gives the clamping range of an ER11 collet as 0.020 inch (0.5 mm) and of an ER16 collet as 0.039 inch (1 mm).[9] That is why collets come in sets: each one covers a narrow band, so plan on one collet for every shank size you run.
Picks that fit2 products
For an ER11 spindle, choose the Genmitsu ER11 15-piece set (101-63-ER11): it adds 1/8 in and 1/4 in collets to the 1-7 mm sizes; the 7-piece set is metric only.
More on choosing
For an ER20 spindle, choose the Genmitsu ER20 14-piece set, 1/16 in to 1/2 in. Neither set fits ER16.
ER11 set with metric and inch sizes
Genmitsu ER11 precision spring collet set, 7 or 15 pieces (1‑7 mm; 15‑piece adds 1/8 in and 1/4 in)
ER20 set up to 1/2 in
Genmitsu ER20 router collet set, 14 pieces (1/16 in to 1/2 in)
The standard behind the name
ER collets are covered by ISO 15488:2003, titled "Collets with 8 degree setting angle for tool shanks - Collets, nuts and fitting dimensions". Its scope covers the dimensions, materials, manufacturing requirements and designation of collets, with their holders and nuts.[10] The standard sets the shape; each maker still publishes its own size table, so read the table for the collet you are buying.
Next
Questions
Can an ER11 collet hold a 1/4 inch bit?
Yes, at the top of its range. The ER11 catalogs checked stop at 7.0 mm, about 1/4 inch, and Command Tool's largest inch ER11 collet clamps 0.231-0.250 inch.[1][12]
Can an ER16 collet hold a 1/2 inch shank?
No. A 1/2 inch shank is 12.7 mm, outside the ER16 ranges Galaxy, Command Tool and Somma publish. You need ER20 or larger.[4][3][2]
Is a 6 mm collet fine for a 1/4 inch shank?
No. A 1/4 inch shank is 6.35 mm, 0.35 mm larger than 6 mm, and REGO-FIX says never to clamp a shank larger than the collet's nominal size. Use a 1/4 inch collet.[7][8]
What does ER20 mean?
It names the collet series size, not the bit. Carbide 3D says the number after ER denotes the size; ER20 collets in the catalogs checked hold shanks up to 13 mm or 1/2 inch.[1][5][6]
Can I put an ER20 collet in an ER11 spindle?
No. The spindle nose and nut are made for one series, so the spindle decides the system. Check the spindle maker's documentation for its collet series.