Wheeler Engineering 72-Piece Professional Gunsmithing Screwdriver SetThe durable bits found in this screwdriver set are made from high grade tool steel hardened to 56 58 Rockwell C. A custom molded box houses the contents of the set which includes: 2 ergonomic driver handles for delivering maximum torque 54 hollow ground bits specifically designed to match the thin slots in gun screws, sizes ranging from approximately . 120 x . 020 to . 360 x . 070 8 Allen bits (1 16, 5 64, 3 32, 7 64, 1 8, 9 64, 5 32, 3 16) 4 Phillips