page_title: Drill bit
section_title: Unibit
hierarchical_section_title: Drill bit / Universal bits / Unibit
caption_attribution_description: English: Two "unibit" drill bits, the smaller one ranging from 1/8" to 1/2" and the larger one scaling to about twice that size.
context_page_description: Drill bits are cutting tools used to remove material to create holes, almost always of circular cross-section. Drill bits come in many sizes and shapes and can create different kinds of holes in many different materials. In order to create holes drill bits are usually attached to a drill, which powers them to cut through the workpiece, typically by rotation. The drill will grasp the upper end of a bit called the shank in the chuck.
  Drill bits come in standard sizes, described in the drill bit sizes article. A comprehensive drill bit and tap size chart lists metric and imperial sized drill bits alongside the required screw tap sizes. There are also certain specialized drill bits that can create holes with a non-circular cross-section.
  While the term drill may refer to either a drilling machine or a drill bit while in use in a drilling machine, in this article, for clarity, drill bit or bit is used throughout to refer to a bit for use in a drilling machine, and drill refers always to a drilling machine.
context_section_description: A unibit (often called a step drill bit) is a roughly conical bit with a stairstep profile. Due to its design, a single bit can be used for drilling a wide range of hole sizes. Some bits come to a point and are thus self-starting. The larger-size bits have blunt tips and are used for hole enlarging.
  Unibits are commonly used on sheet metal and in general construction.  One drill bit can drill the entire range of holes necessary on a countertop, speeding up installation of fixtures. They are often used on softer materials, such as plywood, particle board, drywall, acrylic, and laminate.  They can be used on very thin sheet metal, but metals tend to cause premature bit wear and dulling.
  Unibits are ideal for use in electrical work where thin steel, aluminum or plastic boxes and chassis are encountered.  The short length of the unibit and ability to vary the diameter of the finished hole is an advantage in chassis or front panel work.  The finished hole can often be made quite smooth and burr-free, especially in plastic.
  An additional use of unibits is deburring holes left by other bits, as the sharp increase to the next step size allows the cutting edge to scrape burrs off the entry surface of the workpiece. However, the straight flute is poor at chip ejection, and can cause a burr to be formed on the exit side of the hole, more so than a spiral twist drill bit turning at high speed.
  The unibit was invented by Harry C. Oakes and patented in 1973. It was sold only by the Unibit Corporation in the 1980s until the patent expired, and was later sold by other companies. Unibit is a trademark of Irwin Industrial Tools.
  Although it is claimed that the stepped drill was invented by Harry C Noakes it was in fact first produced by Bradley Engineering, Wandsworth, London in the 1960s and named the Bradrad. It was marketed under this name until the patent was sold to Halls Ltd.uk by whom it is still produced.
caption: A pair of unibits.
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