ACE screwdriver bits are premium， professional-grade power tool accessories. Made to exacting standards， these bits will not let you down. All bits are made from premium S2 tool steel. They are heat-treated and tempered to achieve an optimal hardness of 58-62 HRC， which will absorb shock， reduce twisting and cam-out， while not stripping screw heads. Size tolerances are tightly controlled to ensure consistent and accurate fit.