Klein Tools Designed An Adjustable Screwdriver and Bit Set For The Professional Tradesman and Do-It-Yourself Enthusiasts. All Bits Are Made Of High-Impact Rated S2 Steel With An Optimized Torsion Zone to Enhance Durability By Absorbing Impact Forces. Minimal Chamfering On The Nut Drivers Hex Pockets Increases Surface Contact For Better Performance. All Pieces Fit Into A Durable, Impact-Resistant Case With Steel Hinges, A Stay-Shut Latch, and Modular Stack-Ability With Similar Cases.