Sizes are marked both with a high-visibility laser marking and a permanent stamped marking that won’t wear off, Triple square (XZN) S2 steel bit tips are machined to precise tolerances for strong engagement with fastener heads, Two-piece design allows bit and socket to be optimized separately, for a more durable tool than traditional one-piece designs, Drive end is made of 4140 chromium-molybdenum (Cr-Mo) steel and properly heat-treated for use on impact wrenches, Twist-to-lock socket rail organizes and securely holds sockets in place, both for in your toolbox and on the go.