The wax seals are all the same diameter, but have different thicknesses.
They also have a reinforced wax ring with a rubber insert that helps prevent leaks. I used this on the last toilet in my house I had to reset, it works well.
There are a few other options out now as well besides wax. One is a foam one (I tried it once, did not work, started leaking in a year) and some rubber ones with a thick foam gasket. I just used one of these on my mother in laws toilet, will see how it works.
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