S2 Steel is a premium quality alloy steel for exceptional strength and durability compared with st...S2 Steel is a premium quality alloy steel for exceptional strength and durability compared with standard chrome vanadium driver bits. S2 grade hardened steel for longer life. Driver Bit Size: PH2 Length mm: 150 Shank Dia. inch: 1/4 Shank Type: Hex Material: S2 Hardened Carbon Steel.