Irwin Drill Bits - Step Drill Bits also called UNIBITS step drills 10235 are ideal for drilling holes into thin materials such as stainless steel, copper, brass, aluminum, plastic and laminates. Unibit step drills are made by Irwin. Other unibit step drill bit sizes and type are available upon request. Bisco Tool Supply has for sale Step drills in all sizes.. small drill bits to large drill bits and bulk wholesale quantities are available.