Quoted from dmacy:
What is everyone using for the sling rubber sizes? 2" is the manual and they do fit but they are tight! 2 1/2" seems fine and the originals look to be 2 1/2" but they're old enough that I can't tell for certain.
If using Titan rubbers, most people have shifted to the 2 1/2" rings for the slings.
the titan rubber kits list shows that this is what people are doing.