Not to be “that guy” but cobalt drills are HSS it’s just a blend that has cobalt (5-7%) in it. But it is the better choice for flame/plasma cut holes. Don’t go at them with a carbide bit. Carbide will cut really hard stuff but it’s super brittle using it in a screw gun on a rough hole has a high likely hood of chowdering up the cutting edge in a hurry!