Most of the descriptions from the various suppliers are about the same, although some will run a little larger or smaller. Your best bet would be to find a scale and measure the rats you're currently giving your snake, then compare it to the descriptions from the various companies. Rodent Pro has an excellent size reference page that gives you detailed pictures and gram weights: http://www.rodentpro.com/catalog.asp...el=frozen_rats

I just wanted to mention that a medium rat according to the Rodent Pro site is probably too much food for your Ball. They will have a much more consistent appetite if you keep the size to a weaned or small rat in the 40 gram range even for the largest Ball.