Guys
Does anybody know anything about 5c collets? i have 31 imperial pieces that were bundled with my milling machine but they don't seem quite right and not having much luck on google. They are the same size and dimension of a 5C but no internal thread. The thread at the bottom is left handed and a location groove running down one side from the bottom to the base of the closing slits. There is the same number on all of them (9252) stamped on the lip. Any ideas???

Thanks

Paul