I posted this to the Clausing group on Yahoo, but figured I'd copy it here for anyone who might find it useful. Someone was looking for ER-style collets that they could use in the MT-2 quill of a Clausing 8520 mill, which uses a 3/8-16 internal drawbar thread.
------------------------ It took some digging, but I found the info on my collets. They are from Centaur Precision Tools, Inc. in Miami. (1-800-COL-LETS)The key piece is the collet holder/chuck. They manufacture an ER-25 Collet holder with a MT-2 taper with the internal 3/8-16 drawbar thread. It's not a regular catalog item, but they OEM them for somebody, and they were readily available in July 2001. The guy from the factory that told me about them was named Greg, in case somebody denies they ever existed. They also sell collets in a couple of accuracies, the wrench for the chuck, and even a nice wooden box to hold all the pieces. Because the collets cover a wider range than a normal MT-2 collet, in theory one could get an entire set and be able to hold drill bits of any size. I've listed the pieces I got below, with 2001 prices. They had to be ordered through a local distributor.
#525-117 MT 2 RD25 Inch Thread collet chuck $95.00
#22125 Rd 25 E Wrench $15.50
#WBXRD25 Wooden Box RD 25 (15 collet cap.) $30.00
#250-503 1/8" collet $24.15
#250-505 3/16" collet $24.15
#250-507 1/4" collet $24.15
#250-511 3/8" collet $24.15
#250-515 1/2" collet $24.15
#250-519 5/8" collet $24.15
There are two different collet precisions, standard and high precision. According to the catalog, the TIR for standard precision collets below 0.394" is 0.0006". Above that, it goes up to 0.0008". The high precision collets have half the runout. The catalog lists only standard precision part numbers for the inch collets, but claims that high precision ones are available. I tried to order high precision collets for 1/4" & above, but the dealer shipped (and charged me for) standard precision. I suspect the high precision ones are special order.
You can shop around and get collets cheaper elsewhere, but I was so thrilled at finding some place that would sell me a chuck for my 8520, I decided to reward them with the extra business.
The bad news is that I haven't had time to install the chuck and use it. I got engaged, married and moved since then, and am only now getting my shop set up again.