This Boa professional set of bolt extractors are like nothing you have ever used. These Grabits will quickly and safely remove all types of bolts and as with all the Boa products, the ease of the use will surprise you. These sets will do exactly what you want, they fit deep sockets, quick-change chucks and are efficient in time and performance. Great for use in Engineering, Automotive, Marine, Aerospace. The winslow tip even allows removal of bolts broken below the surface. Works with all standard variable drills. Fits: Drill-Out 1/4in: Bolt size 1/4in / Bolt shank Ø6mm (0.250in)Drill-Out 5/16in: Bolt size 5/16in / Bolt shank Ø8mm (0.312in)Drill-Out 3/8in: Bolt size 3/8in / Bolt shank Ø10mm (0.375in)Drill-Out 1/2in: Bolt size 1/2in / Bolt shank Ø12mm (0.500in)