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 We are definitely in the realms of educated guesses here, rather than absolute certainty, but that's never stopped me before! |
However, from 1934 to 1938, Plimpton labelled their BAYKO conversion sets 1A, 2A, etc., almost certainly because the earliest sets were initially referred to as Accessory sets. |
A for Accessory? |
When the 'New Series' sets emerged in 1939, the conversion sets were completely different from those above and so had to be distinguishable and were called 1C, 2C, etc. |
C for Conversion? |
Post-war sets changed again, so a further distinction was needed. Plimpton went to the back end of the alphabet and the conversion sets were called 0X, 1X, etc. |
X for eXtra, eXpand or eXtend? |
Finally MECCANO simply slipped back into their own familiar terminology and named their conversion sets 11C, 12C, etc. - |
C for Conversion? |
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