pipe exspanshion

Actually, if you were to go the parts store and buy an aftermarket exhaust system, for, say, a Honda Accord EX, you'd find that the parts, going from front to back are "swedged" or "expanded" to allow the preceeding piece to slide inside the next one to be clamped. All air/hydraulic pipe benders, such as the ones an exhaust shop will have such a device to "swedge" open a part. This makes the parts easier to clamp or weld together. So, if you want the exhaust shop to "swedge" open the exhaust pipe to fit over the muffler or vice versa, go for it.