![]() Metric drill bit sizes have many advantages over imperial drills, including more precise hole sizing.įurthermore, you can purchase metric drill bits even in the U.S., and many are listed on packages as metric sizes. For this reason, designers generally want the size of the drill bit to be within 10% of the arbitrary hole size.ĭespite the differences in measurement systems, metric drill bits are compatible with imperial drills. ![]() The smaller size corresponds to a smaller tolerance for the drilled hole’s diameter. ![]() The British Standard BS 328 specifies 230 sizes, ranging from 0.2 to 25.0 mm. Likewise, standard sizes are defined by standards organizations. Typically, a metric drill bit size is defined by its diameter in standard metric lengths. Electrical professionals often use long bit sizes to drill through finished walls to run wires. Typically, fractional bit sizes are used when drilling through very thick materials, such as masonry. In the imperial system, drill bits are sized in 1/64-inch increments, while metric sizes are based on the diameter of the solid metal shank. Typical fractional drill bit sizes are a result of a standard sizing system. For example, a drill bit size of one inch is described as a “B”. Some sizes overlap, such as 1/8″ or 1/64″. While imperial and metric are the most commonly used measurements, drill bit sizes are classified by size. The difference in metric and imperial sizes between drill bits is more confusing than it seems. But how can you determine which drill bit to use? Listed below are some common differences between metric and imperial sizes. While the differences aren’t significant when drilling wood, they can be convenient in metal drilling. These are slightly smaller than their imperial counterparts, and offer incremental differences in drill diameters. Typically, letter and number bits are smaller than metric and are traceable to nineteenth-century English wire gauges. Similarly, letter gauge drill bit sizes go from “A” to “Z.” The chart below gives the equivalent size in metric and imperial units. Instead, the letters represent the actual size of the drill bit.įor example, the largest letter size is “A”, the next largest size is “B”, and so on. They are not the same size as their metric counterparts. Typical fractional drill bit sizesĭrill gauge sizes in North America are denoted by letter or number sizes. Depending on your needs, you may want to try drilling a few samples of each before you make your decision. The fractional sizes are the most commonly used in masonry drilling, rotary hammer drilling, and rotary core drilling. Listed below are the typical fractional drill bit sizes. If you are considering buying drill bits for your project, you will need to know which ones are metric and which are imperial.
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