There are two types of gauges: number and letter. The size of a drill bit is also referred to as its gauge. Drill Size Chart for Number and Letter Gauges It is important to understand the basics of drill bits, their sizes, and how they are measured to ensure efficient work when the drill is needed. Metric drill bits are measure in millimeters, while standard drill bits are measure in inches. Since there are different standards and representations, we will also have multiple charts, with chart having the diameter both in inches and millimeters.Drill bits come in a variety of sizes, both standard, and metric. You can use such device to easily identify the gauge of your drill bit. The following image shows a typical drill bit gauge (not to scale). It is usually a rectangular plate with several holes corresponding to different drill sizes. If you are familiar with the wire gauge (the circular tool that helps you identify the diameter of a wire), there is also a Drill Size Gauge or Drill Bit Size Gauge. Metric Drill Sizes are straightforward representation with the drill size (equivalent to gauge number) is same as the diameter of the drill size. Here, A is next largest drill bit size then #1 and the pattern continues with Z being the largest. The largest gauge number (for example #107) indicates the smallest drill bit size and as the numbers decrease (#1), the drill bit size also increases.Īfter #1, the gauge number end and letters start with ‘A’ all the way up to ‘Z’. The Number & Letter Gauge drill bit sizes are very similar to American Wire Gauge (only in the representation but not the actual gauge numbers). In the U.S., Fractional Inch and Wire Gauge & Letter are very common whereas in the rest of the World, the metric drill bit sizes are predominant.ĭefined in the ANSI B94.11M-1979 Standards, the fractional inch drill bit sizes start from 1/64 inch and scale up all the way to 1inch with 1/64inch increments. Just like other gauges, the Drill Bit Sizes are also defined as per different international standards. But unlike spade bits, Forstner bit make flat bottoms. This bit also helps you make wider holes, just like spade bits.
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