I measured them as well as a set of Greg Dupree downpipes... the difference was 1/8". If I remember right, the RVM downpipe is approx 2 1/4" ID 2 3/8" OD and the Greg Dupree downpipe is approx 2 3/8" ID 2 1/2" OD. The Greg Dupree pipes are smoother on the inside, but they are also $$$...