Abstract: Surgical instrument for forming threaded openings in bone including a guide instrument and a tap instrument. The guide instrument includes a guide tube defining a circular passage and a first rotational stop member arranged generally along a first radial axis and defining a first circumferentially-facing stop face. The tap instrument is positioned within the circular passage of the guide tube and includes a distal thread cutting portion and a second rotational stop member arranged generally along a second radial axis and defining a second circumferentially-facing stop face. The second circumferentially-facing stop face of the second rotational stop member is positioned in abutting engagement with the first circumferentially-facing stop face of the first rotational stop member to prohibit further rotation of the tap instrument relative to the guide tube to prevent damage to internal threads formed in bone by continued rotation of the tap instrument.