how do you measure the size of the muffler?inside or outside?
sounds stupid i know
bought pair of flowmasters (used) they were to be 3 in 3 out because our muffler shop cant bend anything bigger (for the 426 hemi challenger)
so they show up today and the out side of the tubes is like 2 3/4 so im like what the heck am i spossed to do with these???

Since you say they "showed up" today, I take you didn't have the chance to inspect them before hand, but it sounds like you got duped.

Whether they were measured inside or outside diameter wouldn't matter in this case. The wall thickness isn't enough to make up a quarter of an inch. 2.75 is an available size of exhaust pipe, but is much more uncommon than 2.5 or 3. The easiest way to unload your odd ball stuff, call it something more common.

It should be measured on the inside, the exhaust pipe slides into the muffler, sounds like you have 2.5" mufflers.

99% of the aftermarket highperf mufflers are measured by I.D
dont know how flowmasters are now they used to be pretty tight, if they are as bad in shape now as alot of other mufflers are a 2½ I.D" muffler can easily be misshaped enough to measure out at 2 3/4" O.D with the wallthicknes added