Abstract: A thread cutting attachment for use with conventional type engine lathes for the purpose of semiautomatically cutting threads externally on a workpiece, or with a modified embodiment, internally of a workpiece. Each attachment has structure for securely affixing same to the conventional cutting tool holder of such a lathe. A main body of the attachment has a movable cutting tool holder therewithin. The cutting tool holder is suitably actuated through mechanical means from the energization of a fluid cylinder having a piston with rod extending therefrom. Suitable fluid control structure is connected to this fluid cylinder for actuation thereof under the control of either electrical, pneumatic, or hydraulic control apparatus.