These collets are a set ranging from about 1/4" up to 5/8". The back end seems to be cut to MT2 (female) as a MT2 shaft fits snugly. But it could be some other similar taper. They appear to be of fixed holding diameter, well plus or minus a tad. There is a hole that you insert a pin into to prevent the collet turning on the shaft while the nut is tightened. They are a bit chewed up externally but the internals all look fine. Any input is welcome! Free shipping to lower 48 only.