Size: 21mm single hex (6pt). Designed for loosening and tightening brake caliper screws. When using in combination with a torque wrench, always use the correction factor formula that is etched on the wrench. Use with 3/4"D torque wrench. Manufactured from S45C steel (hardness HRC 38-42) with a black phosphate finish. Other sizes available: 22mm (7340), 24mm (7341), 26mm (7342), 27mm (7343) and 30mm (8537).