Irwin 29-pc Cobalt M-35 Metal Index Drill Bit Sets Constructed of M-35 5 percent cobalt high speed steel for super abrasive resistance in tough metals. Cobalt steel extends cutting edge life and maintains cutting life after resharpening. Extra hard drill for greater wear. 135 split point tip starts on contact, cuts with less force. Removable cartridges: easy to carry bits from case to worksite Pack of 1