Anyone who’s spent a little time in a fab shop knows the value of a step drill. With one of these handy bits you can quickly enlarge a hole to a known size without multiple trips to the bit set to get different drills.
What makes these particularly handy is the fact that they have a small fluted drill bit at the top so they drill the pilot hole for you. Essentially, each one of these bits gives you the ability to drill from 2 to 13 different size holes with a single bit.
Like most step bits, these work best with thin material. Irwin suggests that you’ll get the best results with stainless steel, brass, or aluminum sheet metal, or with plastic and laminates. They’re made of high-speed steel and can be had with a titanium coating for a little more money. Other features include a single-flute cutting edge (for greater control through steps) and a three-flatted shank (to prevent slipping in your drill’s chuck).
An interesting note: According to Wikipeda, the step bit was invented by Harry C. Oakes of Wyoming, VA in 1971 but was introduced to the market in the 1980s by the Unibit Corporation, which is now a part of — you guessed it — Irwin Industrial Tools. So it looks like Irwin’s has some serious legacy when it comes to step bits.
Fractional and metric sizes are available starting at around $18.
Self-Starting Step Drills [Irwin]