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What to Look for when Buying Popular Drill Bit Sets

Drill bits are cutting tools of drilling machines and are used to create cylindrical holes. Bits are held in a tool called a drill, which rotates them and provides axial force to create the hole. Specialized bits are also available for non-cylindrical-shaped holes.

They can be made in any size to order, but standards organizations have defined sets of sizes that are produced routinely by drill bit manufacturers and stocked by distributors. In the U.S. fractional inch and gauge drill bit sizes are in common use. In nearly all other countries, metric drill bit sizes are most common. Metric drill bit sizes define the diameter of the bit in terms of standard metric lengths. Standards organizations define sets of sizes that are conventionally manufactured and stocked. For example, British Standard BS 328 defines sizes from 0.2 mm to 25.0 mm.

In smaller sizes, bits are available in smaller diameter increments. This reflects both the smaller drilled hole diameter tolerance possible on smaller holes, and also the wishes of designers to have drill bit sizes available within at most 10% of an arbitrary size hole.

The price and availability of particular size bits does not change uniformly across the size range. Bits at size increments of 1 mm are most commonly available, and lowest price. Sets of bits in 1 mm increments might be found on a market stall. In 0.5 mm increments, any hardware store. In 0.1 mm increments, any engineers' store. Sets are not commonly available in smaller size increments, except for drill bits below 1 mm diameter. Drill bits of the less routinely used sizes, such as 2.55 mm, would have to be ordered from a specialist drill bit supplier.