Abstract: A tool for use in a groove mill to simultaneously form spaced grooves in the interior surface of a bore with the tool including a shank and a pair of heads mounted thereon in spaced relation and in a detachable, non-rotative manner. Each head includes a plurality of insert pockets and inserts secured therein by screw threaded retainers and notches in one head aligned with the screw headed retainers for the inserts in the opposite head to enable indexing of the inserts without disassembly of the heads.