Mercury prop charts

[tgp***]

http://www.maxrules.com/propindex.html
Found this on the web when looking to determine my pro(I do not have a tach). It 1965 through 1974 and some pre 1965 giudeline on boat length and load, and expected speed for prop pitch and diameter.

Does anyone know what the A1, A2, and A3 mean, on the prop number?
Also there is a an A or a C at the begining of the number, what do they mean.

 

[Bondo]

Re: Mercury prop charts

Ayuh,... I might be wrong, but there's not all that much Code in the Part #s...