The 12G does not mean 1275, it's a casting number for a blank crankshaft core. It could have been machined into loads of different sizes as Guessworks list suggests.
12G's were also made to 1100 sizes among other things.
You won't find a listing for 16B as it's not a part number, it's a material specification. Meaning it's the name for a type of cast iron. EN16B however I am almost sure wasn't used for Mini cranks. EN16T was (and that was the grade for certain Cooper engines), as was EN40B for the majority of cranks as DK pointed out.
****
Ok, so I got that the wrong way around above. EN16T is the more common grade and was used for basic 1275 cranks (and the very last Mk111 Cooper S which was very much de-tuned compared to earlier ones, but in this engine it was also Tuftrided) and EN40B was used for Cooper S cranks as it's a better grade of iron.
Edited by Dan, 24 August 2005 - 08:53 AM.