Twist Drill - 5: Sizes
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WARNING: Machine tools present a safety hazard. Improper operation can result in severe injury. These topics are for non-laboratory study only and are not to be used in conjunction with the operation of any tool or machine described herein. Never use a machine tool without the supervision of a qualified instructor.

Twist drills come in a variety of sizes and available in both inch and metric systems. As a rule drills are marked on the shank noting their size. Before using a drill for the first time, however, it should be measured to verify that a size has not been modified. Standard 118 degree drills are often used for modification.

With today's manufacturing technologies it would be the difficult to say what are the limits to how small or how large a twist drill could be made. American Standard drills have been grouped into three sets and designated as:

Fractional set available from 1/64 (.0156) to 3 1/2 (3.500) inches. (above)

Numbers drills (also know as wire gage drills) ranging from #1 (.228) to #90 (.0059). (left)

Letter system that range from "A" (.234) to "Z" (.413). (below)

Miniature metric drill set range from 0.04 to 0.99 in steps of 0.01 mm. Straight-shank set are available in sizes from 0.5 to 20 mm, steps of 0.02 to1 mm. Taper shanks are available from 8 to 80 mm

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label:Drill, Twist drill, drill geometery, shanks, drill materials, specialty