I see what i did there!
I mean the LENGTH of the axles?
I'm guessing they're 5mm different but where to measure from? (Guess the end to the other end, doh!) but, is it different to measure between different brands?
Axles are the same length for 68 & 73, the plastic spacers make up the difference in BB width
83mm needs a different chainset entirely & is a different axle length, not compatible with the 68/73 variant
Dunno how the axle lengths are measured to determine the difference between a 68/73 & a 83 as it's only the BB with that determines which of the two you'd need
Different manufacturers may have different axle lengths as they can use different crank arm fitments
What are you trying to do? Which cranks on what frame? I'm assuming you're trying to fit some cranks to a frame or need to know which cranks to buy?