Abstract: The waveguide assembly is constructed of interlocked sections of hollow rectangular waveguide which are abutted end to end. In a preferred version the abutted ends of the sections may be interlocked by grooving or dove-tailing the sections along the broad walls of the waveguide in a manner insuring alignment of the broad walls. One of the mated sections has locating tabs extending from its narrow walls. The tabs overlap the narrow walls of the adjacent interlocked section and maintain the narrow walls in alignment by preventing slippage along the dove-tail joint. The dove-tail joint is initially constructed in an open configuration and after annealing, the joint is closed by application of pressure thereto. Either one or both broad wall joints may be closed, and when only one is closed then the opposite joint is initially constructed in a closed position.