I was looking into gears for my other truck (non toyota) and eaton lists various Axle Spline and ring gears. are these #'s always specific to the exact vehicle, and if not, whats the difference?

here is the link I am looking at:

http://www.eatonposi.com/prod5.htm

 

Eaton/GM made many different combinations of axle spline counts and ring gear diameters. You have to know what you have before you can order new gears. You also need to know what gears you currently have because many Eaton carriers/housings will only work with a specified range of gear options.