If you take BSA M20 (ex W.D.)1940-45 276C/1B as stated in Amals reference books 276 is the carb body C tells you it was supplied to bsa from amal also all the sizes of jets slide cutaway then after the / is 1B this is the float chamber this tells you the angle of the float fitted to the carb as if you have the wrong one fitted the carb will flood now if you've got the same carb supplied directly from Amal it will be stamped with an Amal number 276/014R this is the standard Amal body for a 1" carb.
M21 (ex W.D.)1940-45 276P/1B supplied to BSA same carb supplied by Amal becomes /024R right hand body 1 1/16" i have been selling genuine Birmingham Amal spares for the last 40 odd years hope to see some of you soon at a jumble
