Abstract: A handle mechanism adapted for mounting on a manually rotatable shaft of a machine tool. A spring-biased index pin mounted in the handle mechanism is extensible and retractable by movement of an associated handle member to selectively engage and disengage an index plate fixedly attached to the shaft of the machine tool, thereby permitting the handle mechanism to be coupled to the shaft for manual rotation thereof and decoupled from the shaft for independent rotation thereabout. The index pin and its surrounding bias spring are retained within the handle mechanism by a single threaded fastener permitting their ready removal for replacement or repair.