# AltMill 2.2KW ER20 Spindle Nut **URL:** \ **Category:** đź“„ General\ **Created:** [February 5, 2026, 1:20am UTC](https://forum.sienci.com/t/altmill-2-2kw-er20-spindle-nut/25613 "2026-02-05T01:20:17Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![retracbill](https://forum.sienci.com/letter_avatar_proxy/v4/letter/r/3e96dc/32.png) [@retracbill](https://forum.sienci.com/u/retracbill)\ **Post date:** [February 5, 2026, 1:20am UTC](https://forum.sienci.com/t/altmill-2-2kw-er20-spindle-nut/25613/1 "2026-02-05T01:20:17Z")
Does anyone know of a source or the size of the collet nut on the bottom of the AltMill 2.2KW ER20 Spindle? Are these a standard size? I see these on Amazon but not sure about thread sizing. ---
**Author:** ![Chucky\_ott](https://forum.sienci.com/user_avatar/forum.sienci.com/chucky_ott/32/8692_2.png) [@Chucky\_ott](https://forum.sienci.com/u/Chucky_ott)\ **Post date:** [February 5, 2026, 10:52am UTC](https://forum.sienci.com/t/altmill-2-2kw-er20-spindle-nut/25613/2 "2026-02-05T10:52:24Z")
@retracbill I would suspect that they are standard but I can’t say for sure. I purchased a set of four collet nuts for my 1.5kW ER20 spindle from Amazon and they fit fine. The only thing I’ll add is that if you’re paying less than $50, they are most likely not balanced collet nuts. Balanced nuts would have a small dimple drilled into the side when they do balancing. I don’t know if unbalanced nuts could cause issues in the long term. ---
**Author:** ![Chucky\_ott](https://forum.sienci.com/user_avatar/forum.sienci.com/chucky_ott/32/8692_2.png) [@Chucky\_ott](https://forum.sienci.com/u/Chucky_ott)\ **Post date:** [February 5, 2026, 10:54am UTC](https://forum.sienci.com/t/altmill-2-2kw-er20-spindle-nut/25613/3 "2026-02-05T10:54:51Z")
@retracbill Also, if you’d like Sienci to carry them, send them an email. I asked them about stocking some and they said it would depend on customer demand. ---
**Author:** ![Dnick](https://forum.sienci.com/user_avatar/forum.sienci.com/dnick/32/9326_2.png) [@Dnick](https://forum.sienci.com/u/Dnick)\ **Post date:** [February 5, 2026, 2:13pm UTC](https://forum.sienci.com/t/altmill-2-2kw-er20-spindle-nut/25613/4 "2026-02-05T14:13:00Z")
I bought a set of collet nuts for my 1.5kw ER16A M24x1.0 Spindle from Amazon last April for about $14 and they are not balanced, but I only use them for my large router bits (1/4” and up) with the thought the large mass of the bit will offset any imbalance 🤨 . So far, so good 🥴 . There are others (HARFINGTON) that claim to have “Dynamic Balance Holes”, but they do not show up in the pictures… ---
**Author:** ![mick\_s](https://forum.sienci.com/user_avatar/forum.sienci.com/mick_s/32/9655_2.png) [@mick\_s](https://forum.sienci.com/u/mick_s)\ **Post date:** [February 5, 2026, 5:34pm UTC](https://forum.sienci.com/t/altmill-2-2kw-er20-spindle-nut/25613/5 "2026-02-05T17:34:41Z")
The ER20 collet nut uses a 30mm wrench. ---
**Author:** ![DavidB](https://forum.sienci.com/letter_avatar_proxy/v4/letter/d/76d3ee/32.png) [@DavidB](https://forum.sienci.com/u/DavidB)\ **Post date:** [April 28, 2026, 2:51am UTC](https://forum.sienci.com/t/altmill-2-2kw-er20-spindle-nut/25613/6 "2026-04-28T02:51:47Z")
@Chucky_ott Are you able to provide link or mention name to known balanced ones? ---
**Author:** ![Chucky\_ott](https://forum.sienci.com/user_avatar/forum.sienci.com/chucky_ott/32/8692_2.png) [@Chucky\_ott](https://forum.sienci.com/u/Chucky_ott)\ **Post date:** [April 28, 2026, 7:18am UTC](https://forum.sienci.com/t/altmill-2-2kw-er20-spindle-nut/25613/7 "2026-04-28T07:18:18Z")
@DavidB User @tda from Precise Bits posts a lot of useful information on this site. It looks like they supply collet nuts in the States. > **[ER Collet Nuts and Wrenches](https://www.precisebits.com/products/equipment/er_colletnut.asp)** > > ER collet nuts balanced to G2.5 for 20,000 RPMs. ER wrenches with castle design for high-torque tightening and purely tangential tightening torque. ---
**Author:** ![AJEAN](https://forum.sienci.com/letter_avatar_proxy/v4/letter/a/3be4f8/32.png) [@AJEAN](https://forum.sienci.com/u/AJEAN)\ **Post date:** [May 2, 2026, 5:51pm UTC](https://forum.sienci.com/t/altmill-2-2kw-er20-spindle-nut/25613/8 "2026-05-02T17:51:17Z")
Anybody has a good source in Canada for ER20A balanced nuts ?