Question about Collets

Ive done woodworking for ages, so I guess this question is based on that experience.

Are collet holders standardized on spindles? I see endmills with all sorts of shank sizes (Not the 1/4 and 1/2) I am used to.
So, I see ER11 has a range of 0.02 to 0.3125 inches, which doesn’t equate to a very large endmill.

Second question:
Assuming a spindle comes with an ER11 collet, can I put say an ER20 collet on it? How would I know what size collets a spindle can take or do they all take from ER8 to ER50 (I doubt it, but I’m really confused here).

If a spindle is designed for an ER11 collet then only ER11 collets will fit. Each specific shank size (1/16, 1/8, 1/4, 4mm, 6mm) will require a new ER11 collet. But as you have noticed it is not possible to have a 1/2 inch ER11 collet.

To use 1/2 inch shank tools you would need a spindle that accepts ER20 collets.

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