Features: Reverse spiral flutes are designed to bite down to provide maximum gripping power Useful for trying to free rounded-off, rusted-tight or painted-over bolts Made from Chrome Vanadium Steel Specification: 1/4" - 6.0mm 5/16" - 8.0mm  3/8" - 9.5mm 7/16" - 11.0mm 1/2" - 12.7mm Drive size: 3/8" Includes 3/8" Drive to 1/4" Hex adaptor