IVY Classic 44472 1-Inch x 5/16-Inch Hex Tamper Resistant Insert Bit, Impact Plus, 1/Box High-grade S-2 Tool Steel for extra strength and durability Designed to withstand the high torque (rotational force) of impact drivers, Impact Plus (Registered Trademark) Heat treated and tempered to Rockwell Hardness 60 - 62, sandblasted finish prevents rust Precision machined for ideal fit and superior holding power Length: 1-inch, Size: 5/16-inch Hex, Shank: 1/4-inch hex, Sturdy reusable snap lock box