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.
@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.
@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.
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…
The ER20 collet nut uses a 30mm wrench.
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