ER-collets are a de facto industry standard and are manufactured by a wide variety of companies, and sold by many more. Based on an initial offering by Rego-Fix which was adapted from an earlier standard:
The design was patented by Rego-Fix in 1972, and later standardized as DIN 6499.
The Wikipedia article has some information:
@TDA was generous enough to write up a bit on this previously:
(note that that post links back to this thread — I’d suggest reading both threads in their entirety)
and the company which he represents/works for offers sizes of collets which match all of our machines, and in run-out/balance specs to suit any shop’s needs (and budget):