KnKut Hard Steel Drills are Carbide Tipped and made for use in drilling hardened steel in the range of 48 to 65 Rockwell "C". Holes may be drilled without annealing or appreciably changing the structure of the material. This drill bit can be used for drilling BROKEN STUDS, SPRING BOLTS, DIE SECTIONS, BROKEN EASY OUTS, EXTRA TOUGH METALS, EXOTIC METALS, BRAKE DRUMS, ETC. Set Includes 1pc each 1/8", 3/16", 1/4", 5/16"x 4, 3/8" x 4NOTE: Heavy Pressure and low R.P.M.'s recommended. Cutting oil should be used. Recommended for use in drill presses, but can be used in portable drills.Use KnKut Hard Steel Drills to drill:Broken Studs, Spring Bolts, Die Sections, Broken Easy Outs, Extra Tough Metals, Exotic Metals, Brake Drums, Broken Taps