Metallics HSSCBLK29 Drill Bit HD Cobalt St 135d SplPt 1/2" 6" Black (1pc)

Cobalt high speed steel is the reason to pick this one. The HSSCBLK29 is a heavy duty cobalt bit at 1/2 inch diameter with a 135 degree split point, which is the geometry used for stainless, abrasive alloys, and work hardened metal because it starts cutting on contact instead of walking. Run it slow with cutting fluid and steady pressure on stainless so you cut chips rather than polish the hole.

It has a straight shank at the full 1/2 inch cutting diameter, so you need a chuck that opens to a true 1/2 inch. Most 3/8 inch keyless chucks on compact cordless drills won't take it. A 1/2 inch chuck drill or a corded drill with low speed and high torque is what you want anyway for a half inch hole in steel.

For a single clean 1/2 inch hole in enclosure sheet metal, a step bit or a knockout punch is usually the better choice, since a twist bit this size tends to grab and triangulate thin gauge steel. Where this 1/2 inch cobalt bit earns its place is thicker material: strut, angle iron, plate, stainless brackets, and hardened fasteners being drilled out. Its 135 degree split point is what lets it bite hard metal without a pilot hole wandering.

One piece, supplied in a pouch. The HSSCBLK29 is a single 1/2 inch cobalt bit, so if you need a range of sizes for an electrical rough-in you'll be ordering each diameter separately rather than getting an indexed set.

The black oxide style surface on the HSSCBLK29 is a dark finish over the cobalt steel body. It reduces friction and helps with heat and corrosion resistance in ferrous metal work. Note that the cutting ability comes from the cobalt alloy itself, not the coating, so the bit keeps cutting even after the finish wears off the lands and it can be resharpened.