NEC 344
Rigid vs EMT Couplings: Threaded, Set-Screw, and Compression — Which Coupling for Which Raceway
EMT set-screw, EMT compression, rigid threaded, and rigid threadless compression couplings: what each joins, why EMT and rigid fittings never interchange (different ODs), and the NEC 344.42 / 358.42 bonding rules.
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