New to forumn, have some exhaust ?'s

[IOWNATRUCK]

Hey everyone I just joined yesterday and im hoping il be able to get some help and also help a few people out. Im sorry if this thread is a bit repetitive as i have looked through everything but couldnt find anything with the answers i needed. Ive got a few questions and okay here it goes, Ive got a 1984 Chevy C10 Stepside and im getting dynomax bullets, Ive measured the circum. of the exhaust pipe in two different places ( one was a bend so it was a bit smaller) and i got 8 and 7.5. So i divided by pi and i believe i had gotten 2.55 and 2.39, I dont have a caliper and I was wondering if the numbers mean my truck has a 2.5 inch od? Because im sure a tape measure wasnt 100 percent accurate. if anyone has the same truck any answer will be appreciated. I also am ordering lap joint band clamps and i was curious as to what size i would need? because if the exhaust od is 2.5, and the id of the muffler is 2.5, would i need a clamp that is 2.5- 2.75? If so, ive looked and couldnt find one that says the sizes definitively, any help is appreciated, sorry its so long.
Thanks. Oh, and also if the muffler i order is a 2.5 inch id for say, would i order the 2.5 inch od pipe for the tail pipe?
Thanks.