| Here is an enlarged scan of the various 3" pulleys, part 19b, that I have found in various US Meccano outfits. It has recently been discovered that US Meccano used a slightly different size screw than British Meccano, at least after around 1920. The black four-spoke version in the upper left has the British 5/32 BSW thread. Unless noted, all of the others are tapped #7-32, a US thread which apparently became obsolete around 1935. Those labeled with #6-32 set screws are from Gilbert Meccano outfits, and were made by Gilbert. All of these have a single tapped hole for the set screw. About 1928, British production started coming with two tapped holes, diametrically opposite; this is known as "double tapping". It seems that all US production was "single tapped." |
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