Abstract: A safety lock ring for a circular tool, such as a sawblade, comprising a first collar with a generally cylindrical body portion and a flange engaging one side of the tool, a circular, split tool, such as a sawblade, comprising a plurality of separate segments and having a central opening, when assembled, through which the body portion of the first collar extends, and a second collar disposed around the first collar body portion and having a tool-engaging surface on the opposite side of the tool. A pair of annular grooves on opposite faces of the tool are in interlocking engagement with corresponding annular ribs on the first and second collars, respectively, and the first collar is urged against the tool face so as to clamp the tool between it and the first collar by means of an outer locking collar threadedly secured to the first collar body portion. Dowels, press set in the flange of the first locking collar, extend into openings in the tool segments so as to key the segments to the flange.