it is this type of o-ring, double seal, with the proper size when the lips are compressed it is just a hair bigger ID then 15mm and the OD fits perfectly around the intake and the back metal part of the clamp creating a solid path for air fuel mixture to pass. literally sit there and drowned that spot in carb cleaner and with no hiccups.
And according to the specs when its squished down it only .070" thick, so it wouldn't cause problems.
and it comes with a size 64-70 or 76-84 of your choice and i think 2.17 atomizer. I'll check tomorrow and give a more complete list of jet sizes i can provide. (edited)