I still have my Megan header installed, but everything else is stock cat --> stock piping and muffler --> AP2 fancy exhaust tip
so with that in mind, the flanges need to be the same size as oem.
and I guess they are based on that?
I need to look under my car and make absolutely sure it's my cat causing the exhaust leak I've been having, I swear that stock oem cat was terrible from the start. I'm pretty sure it is, I'll look for fumes when I check tomorrow.