Sizing difference between an eggbutt and loose ring?

[spotty_pony]

As title. Do I have to go up/down a 1/4 mm for an eggbutt? It's an NS one if that makes any difference!

Thanks

 

[Sugar_and_Spice]

Loose rings need to be a fraction bigger so the lips aren't pinched in the hole between the rings and mouthpiece.