Guide · Collets and collet nuts
ER11 collet sizes and the 1/4 inch limit
ER11 collets stop at 7 mm, about 1/4 inch. Maker size tables, how much each collet closes, set contents and the two ER11 nut threads.
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Picks that fit
- Genmitsu ER11 precision spring collet set, 7 or 15 pieces (1‑7 mm; 15‑piece adds 1/8 in and 1/4 in)Check price on Amazon
- Genmitsu ER11‑A collet clamping nuts, 4‑pack (M14 thread)Check price on Amazon
Short answer
The largest ER11 collet holds about 1/4 inch. Galaxy, Command Tool and Somma all stop at 7.0 mm, and Command Tool and Somma stop at 1/4 inch.[1] Each ER11 collet closes only about 0.5 mm, so you need one collet per shank size, and the nut must match your spindle's thread.
Picks that fitAll picks and how to choose
- Genmitsu ER11 precision spring collet set, 7 or 15 pieces (1‑7 mm; 15‑piece adds 1/8 in and 1/4 in)Check price on Amazon
- Genmitsu ER11‑A collet clamping nuts, 4‑pack (M14 thread)Check price on Amazon
ER11 is a collet size, not a shank size
The "11" in ER11 names the collet series. It does not mean an 11 mm bit fits.[1] On a hobby CNC, ER11 is the small end of the range: fine for 1/8 inch and 1/4 inch bits, and nothing larger.
Maker size tables
Each maker publishes its own list. They agree on the top size and differ at the bottom.
| Maker | Smallest | Largest | Notes |
|---|---|---|---|
| Galaxy | 1.0-1.5 mm (ER11-015) | 6.5-7.0 mm (ER11-070) | 15 sizes in total |
| Command Tool (metric) | 0.5-1.0 mm (ER11-0100) | 6.5-7.0 mm (ER11-0700) | |
| Command Tool (inch) | 0.106-0.125 in (ER11-F125) | 0.231-0.250 in (ER11-F250) | |
| Somma | 1 mm and 1/16 in | 7 mm and 1/4 in | Sold in metric and inch sets |
Galaxy's table runs from 1.0-1.5 mm to 6.5-7.0 mm, 15 sizes in total.[2] Galaxy's drawing fields list D 11.5 mm and length 18 mm for its ER11 collets.[2] Command Tool's metric ER11 collets run from 0.5-1.0 mm to 6.5-7.0 mm, and its largest inch ER11 collet, ER11-F250, clamps 0.231-0.250 inch.[3]
How much one collet closes
An ER11 collet grips a narrow band of sizes. PreciseBits gives the clamping range of an ER11 collet as 0.020 inch (0.5 mm).[4] Somma states a .019 inch collapse range for its ER11 collets, smaller than the 1/32 inch it gives for its larger non-sealed series.[5]
That is why sets exist. Somma's metric ER11 set has 13 collets from 1 to 7 mm in 0.5 mm steps, and its inch set has 7 collets from 1/16 to 1/4 inch in 1/32 inch steps.[5] If you run both inch and metric bits, you need collets from both lists.
1/4 inch is not 6 mm
A 1/4 inch shank is 6.35 mm, so it is 0.35 mm larger than a 6 mm shank.[6] A 6 mm ER11 collet is the wrong part for 1/4 inch bits. Buy a collet made for 1/4 inch.
Picks that fit1 product
Choose the 15-piece set (101-63-ER11) if you run inch bits: it adds 1/8 in and 1/4 in collets to 1-7 mm in 0.5 mm steps.
More on choosing
The 7-piece set (101-60-70ER11) is 1-7 mm in 1 mm steps with no inch sizes.
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)
Two ER11 nut threads
The nut has to match the spindle nose. PreciseBits lists standard ER11 nuts with an M14 x 0.75 thread and ER11 mini nuts with an M13 x 0.75 thread.[7] A nut labeled only "ER11" may be either, so check the spindle maker's documentation or the old nut before you order. More in ER collet nut threads and mini nuts.
Picks that fit1 product
These are ER11-A nuts with a 14 mm thread (SainSmart does not state the pitch). Buy them only if your spindle takes the standard M14 ER11 nut, not the M13 mini nut.
Genmitsu ER11‑A collet clamping nuts, 4‑pack (M14 thread)
Who uses ER11
Carbide 3D's ER-11 Compact Router uses standard ER11 collets, ships with 1/4 inch and 1/8 inch collets plus a nut and wrench, and lists 1/4 inch as its maximum cutter shank.[8] Sienci's AutoSpin uses ER11 collets for tooling up to 1/4 inch.[9] For bits with a larger shank, the spindle itself has to change to a larger series.
Next
Questions
What is the biggest bit an ER11 collet holds?
About 1/4 inch. Galaxy, Command Tool and Somma all stop at 7.0 mm, and Command Tool's largest inch ER11 collet clamps 0.231-0.250 inch.[1][3]
Do I need a separate ER11 collet for every bit size?
For practical purposes, yes. PreciseBits gives an ER11 collet's clamping range as 0.020 inch (0.5 mm), and Somma states .019 inch for its ER11 collets.[4][5]
Which ER11 nut fits my spindle?
The one that matches its nose thread. PreciseBits lists standard ER11 nuts at M14 x 0.75 and mini ER11 nuts at M13 x 0.75; check your spindle maker's documentation for which one it uses.[7]
Can I use a 6 mm ER11 collet for 1/4 inch bits?
No. A 1/4 inch shank is 6.35 mm, 0.35 mm larger than 6 mm. Use the 1/4 inch collet.[6]