I bought some Whitworth thread size guages at Ally Pally yesterday and am puzzled by part of the markings. They all have a number followed by G. The number is clearly the number of teeth per inch but what does the G represent? A few of them also have other numbers after the G, such as 48G
Cliff Coggin Kent UK
G stands for Gauge an abbreviation of tpi. They have been putting these on thread gauges [ G ? ] for so long the history has been lost. Same for the sizes 7G 1-1/8 and 1-1/4 should read 1-1/8" and 1-1/4" as both these sizes share the 7 pitch. These are only good for the Whitworth range and although the gauges are good for BSF, BSP etc the diameter numbers don't relate only the pitch.
They would be better off just marking the pitch only on them and leaving the rest for you to determine with a set of tables.
-- Regards,
John Stevenson Nottingham, England.
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Many thanks John.
Cliff.
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