All the kits want to give you one or two inserts that are like .684, and .686, but personally, I've never used those sizes. Most paint I use is between .689 and .693
depends on the paint you shoot i guess, the severe we shoot all tends to be a little small compaired to some other brands (eg rps and zap which tend to be on the big side)
i just bought a pair of st!ffis in 0.689 and 0.687 i might even so one smaller and get a .685 too, quite likely to get a .691 as well tho for the odd batch thats a bit bigger although ive never had any probs using standard .688 boomsticks in the past
Marb may have grown bigger. I haven't shot RPS in a while, but I do remember the stuff rolling out of my .689 barrel and thus using a .686 to keep it in place. It could have been a "different" batch/cold weather, etc. But this stuff sure was small.
If your usin zap chronic or ultimate the perfect size is the 689 at the minute,
but i have had to use a 691 for the chronic and a 687 for the ultimate in the past.