If I have a 3" exhaust do I need a 3" clamp or 3 1/4" clamp or 2 3/4" to make sure it's tight?

Do these have a habit of leaking?

I just need a way to make my y-pipe easy to remove and I don't have the money, time, or welder to put a flange on.

Thanks

 

I have a 3" cat back with stock y-pipe and picked up a 3" band clamp. The clamp is too loose, I think that a 3" clamp means that 3" is the smallest it goes down to. I need to pick up an 2.75" one to get things tight. It was easy to put on though.

 

I dont know on the sizing, but they dont leak. Mine has been on for a long time with no issues.

 

This one time at band clamp.............................