A few of us on this earth have mills that don't use R8 collets. My old US Machine Tool Co vertical mill has a B&S #9 spindle and they often came with Collet adapters for the following double angle collets, so:
For those of you who use double angle collets made by Universal Tool, the Y, Z and ZZ, for instance, here are a couple of sites that have them:
I went to google and typed in (using the quotes) "z collet" I got 608 hits and these were the first two. Here are two sites that have Z (and other) collets for sale:
Not all sizes, but many of the ones one might use.
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Go to page 19 see what they have and call, I guess, to order.
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Pete Stanaitis
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