Abstract: The adaptor is to enable a cutting tool holder such as a boring bar to be mounted on a standard arbor having an internally screw-threaded boss and drive keys. The adaptor comprises a thrust ring, a retaining screw and a spacer. The thrust ring has a multiplicity of internally tapered recesses in its peripheral surface and is rotatably mounted on the arbor by the retaining screw. Rotation of the thrust ring is permitted to enable alignment of a respective recess with a respective locking screw in the cutting tool holder.

Abstract: A cutting tool has a body with an external screw threaded portion on which is mounted an internally screw threaded adjustment ring, a disc spring, a tapered collet having a frusto conical surface and a clamping member. The frusto conical surface is adapted to be engaged against a frusto conical recess in a tool holder having a bore therein in which said body is insertable. The body is adjustable axially of the tool holder by rotation of the ring and then clamped in position by the clamping member such as a bolt. A key engaged in a keyway prevents rotation of the body relative to the tool holder. The cutting tool is thus lockable relative to the tool holder firmly and accurately.