I can measure one for you, but, I don't know for sure how they are measured. When I ordered a set of 30 spline axles, I just told the guy that I wanted a set of axles for a G-body with a 8.5" rear and he knew what they were....that was Moser.
I'll second that! They were about $20 less than moser. I also got a T/A cover from them for $135!ULYCYC:
Call Gears R Us they seem to have the best price.