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