Adaptors for a collet chuck

In a collet chuck assembly including a selected collet for a pre-selected drill size and a collet nut for a collet chuck wherein the collet chuck has an inside taper which mates with the outside rearwardly extending taper of the collet and the collet nut has an inside taper which mates with the outside forwardly extending taper of the collet, the improvement comprising a set of first and second adaptor rings, each adaptor ring having an inside frusto-conical surface and an outside frusto-conical surface parallel to the inside frusto-conical surface, said first adaptor ring having an inside taper complementary to the outside forwardly extending taper of the collet and an outside taper complementary to the inside taper of the collet nut and said second adaptor ring having an inside taper complementary to the outside rearwardly extending taper of the collect and an outside taper complementary to the inside taper of the collet chuck and wherein said adaptor rings enable use of any of a plurality of selected collets for a wide range of pre-selected drill sizes in a single collet chuck.