Guide · Collets and collet nuts
ER collet nuts: standard vs mini threads, and finding yours
Standard and mini ER11, ER16 and ER20 nuts use different threads, so the series name alone does not identify a nut. Thread table and what makers say.
We may earn a commission if you buy through links on this page. How we make money
Picks that fit
- Genmitsu ER11‑A collet clamping nuts, 4‑pack (M14 thread)Check price on Amazon
Short answer
An ER nut must match your spindle's nose thread, and the series name alone does not tell you which thread that is. Each of ER11, ER16 and ER20 comes as a standard nut and a smaller "mini" nut with a different thread.[1] Check the spindle maker's documentation, or the nut you already have, before you order.
Picks that fitAll picks and how to choose
- Genmitsu ER11‑A collet clamping nuts, 4‑pack (M14 thread)Check price on Amazon
Standard and mini threads
PreciseBits publishes the thread for each ER nut type. The standard (hex, standard or UM) nut and the mini nut differ in diameter, and for ER16 and ER20 in pitch too.[1]
| Series | Standard nut thread | Mini nut thread |
|---|---|---|
| ER11 | M14 x 0.75 | M13 x 0.75 |
| ER16 | M22 x 1.5 | M19 x 1.0 |
| ER20 | M25 x 1.5 | M24 x 1.0 |
So a nut labeled only "ER20" does not identify which spindle it fits.[1] The collets inside are the same series; the nut and the spindle nose are what change.
A real example: Carbide 3D's ER16M
Carbide 3D's 65 mm ER16 VFD spindle (updated May 2025) uses an ER16M collet nut with an M19 thread.[2] Its kit ships 1/8, 1/4 and 3/8 inch ER16 collets with that ER16M nut.[3] M19 matches the ER16 mini thread in PreciseBits' table, not the M22 standard nut. An ordinary ER16 nut will not thread onto that spindle.
How to find your thread
- Look up the spindle in its maker's documentation. Many makers name the nut type (for example "ER16M") or the thread.
- If you still have the original nut, look for a marking on it, or ask the spindle maker.
- Order a nut that names the same series and the same thread. If a listing says only "ER11" or "ER20", ask the seller which thread it is before you buy.
Picks that fit1 product
These ER11-A nuts have a 14 mm thread (SainSmart does not state the pitch; the standard ER11 nut is M14 x 0.75).
More on choosing
Choose them only for an ER11 spindle that takes the standard M14 nut, not an M13 mini nut.
Genmitsu ER11‑A collet clamping nuts, 4‑pack (M14 thread)
What the nut's lip does
The inside of an ER nut is not just a thread. Carbide 3D explains that the off-center lip inside the nut is a retention feature: it traps the collet so the collet comes out of the spindle taper with the nut.[4]
That only works if the collet is seated in the lip first. Carbide 3D says to snap the collet into the nut before inserting a tool, because a tool already in the collet keeps it from seating in the retention ring.[4] Carbide warns that skipping this can push the collet off-center and damage the spindle and collet. The full sequence is in seating an ER collet and bit.
Low-profile nuts
Some makers sell slimmer nuts for tight spaces. REGO-FIX names its Hi-Q/ERM and Hi-Q/ERMX clamping nuts as options for minimal external dimensions.[5] REGO-FIX does not list their threads on that page, so check the thread against your spindle like any other nut.
Tightening: two makers, two cautions
Makers disagree on how much to say about torque. REGO-FIX recommends tightening its clamping nuts with a torque wrench and publishes its tightening torques as a separate download.[5] PreciseBits cautions that its ER nut torque values may not always be required, preferable or even possible, and treats maximum torque as a warning rather than a recommendation.[1]
We do not publish a torque figure. Use the wrenches and instructions your spindle maker supplies, and the torque values of the nut's own maker if it publishes them.
Next
Questions
Are all ER20 nuts the same?
No. PreciseBits lists standard ER20 nuts at M25 x 1.5 and mini ER20 nuts at M24 x 1.0. A nut labeled only ER20 does not tell you which spindle thread it fits.[1]
What is an ER16M nut?
A mini ER16 nut. Carbide 3D's 65 mm ER16 spindle uses an ER16M nut with an M19 thread, which matches the M19 x 1.0 thread PreciseBits lists for ER16 mini nuts.[2][1]
Do I need a torque wrench for an ER nut?
REGO-FIX recommends tightening its nuts with a torque wrench and publishes torque values separately. PreciseBits cautions that its torque values may not always be required, preferable or even possible, and treats maximum torque as a warning. Follow your spindle maker's instructions.[5][1]
Why does the collet come out with the nut?
Carbide 3D explains that the off-center lip inside an ER nut traps the collet so it leaves the spindle taper with the nut.[4]