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7-Threads, Taps, and Tapping - Machine Screw Taps

Machine screw taps, both hand and machine, are smaller than a 1/4 (.250) inch and designated by a number rather than a fraction nomenclature.

These numbers range from 0 to 12. For example the smallest size (0-80) diameter is about .060 and has 80 threads to the inch.

The largest size is 12-28 and the diameter is about .216 with 28 threads per inch.

With the exception of the number in place of the fraction, the Alpha Numeric Identification scheme remains the same. The tap drills are derived the same way as the fraction drills are.

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