Description 41945, 41964, 41971, 41979, 41987, 41992 Need help? Here’s a quick lesson on automotive exhaust pipe sizing. – Components such as mufflers, catalytic converters and resonators are generally measured in I.D. sizes. – Pipes such as extension pipes and tail pipes are measured in O.D. sizes. Although both part types possess the same advertised diameter, pipes are meant to slide into components.
