Abstract: A gear cutting tool has a series of separate cutter inserts removeably clamped to the front ledge of a holder block. Each cutter insert has a forward cutting edge that extends beyond the ledge and a rear positioning portion that includes a central projection extending rearwardly from side faces. The central projection mates with a respective one of a series of parallel tracks formed in the holder block and the rear faces mate with upright front walls at the rear of the ledge on either side of the track. The arrangement precisely locates the cutter insert in the holder block. The holder block may be formed of a single piece or may be built up of identical interlocking block elements.