As a piping engineer, purchaser, or installer, have you ever been confused when selecting grooved couplings: you order a DN100 coupling, but the supplier asks to confirm if the pipe’s outside diameter is 108mm or 114mm? Similarly, a DN150 pipe could have an OD of 159mm or 168mm. This is not a manufacturer error. It is a direct result of the coexistence of different pipe standard sy... https://www.furdfittings.com/decoding-grooved-couplings-a-full-analysis-of-pipe-standard-variations/