Number and letter gauges for drill bits do not follow a formula or standard increments. The wire gauge and letter systems refer to tool diameters that increase as the wire gauge decreases from #107 to #1 and then continues from A to Z. Fractional sizes are measured in inches, while metric sizes are measured in millimeters.The second and third columns show the decimal equivalents of the diameters are shown in both English and Metric units.This table is split up into 4 sections as it would make a very long list on the page otherwise. The first shaded column shows fractional, metric, wire gauge number, and letter columns.The drill size chart below provides a list of standard size drill bits in several measurement systems.The drill bits that I use every day range in size from 0.8 mm (0.0025 ct) to 5.0 mm (0.50 ct) in diameter and I tend to buy them in the sizes closest to the gems I set. for me, as a general rule, I tend to buy my drill bits in sizes that allow me to set round gems. I personally rarely ever use one over 5mm in size. I will not go into that as most jewelers use very small drill bits. But I decided that I should include additional information as it makes the discussion complete.Ī common standard for metric drill sizes is the Renard series, which uses a simple factor to determine the diameter. Aircraft-length drills are extended length drill bits that are manufactured in fixed length such as 4, 6, 8, 12, 18, 24-inch bits, rather than proportional lengths.As a jeweler you really should be using metric drill bits.They are used primarily in machinist workshops for screw machinesand are not usually available in hardware stores. Screw-machine-length drills arethe shortest available standard sized bits.
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