Abstract: A lathe tool holder has a straight supporting arm and a clamping outer end formed by slotting the outer end in a horizontal central plane to define clamping jaws having opposed dovetail portions which when urged together by a clamping screw grip a resilient tool bit adapter having sides compressible by the jaws to grip a tool bit. Different tool bit adapters are used having socket-like bit-receiving openings which are either parallel to the plane of the slot in the holder or inclined with respect thereto, depending upon the type of work or direction of cut. A drilled hole extends vertically entirely through both jaws, and is tapped to form threads therein which lie on a nominally continuous helix, to receive the clamping screw. The clamping screw is threaded at its end remote from the head for a length which does not exceed the thickness of a single jaw.