One curious characteristic of this series is that the screw diameters were defined in millimeters, but the pitch in threads per inch. The Waltham Watch Company, in Waltham, Massachusetts, was a major manufacturer of watches.
|No. of threads
|Diameter of thread,
|Diameter of tap drill,
Source: Machinery, vol. 22 (March 1916), page 590.
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Last revised: 18 January 2011.