Abstract: First and second members 1a, 1b, each having a U-shaped groove 20 of identical width and length, are joined together so as to constitute a waveguide channel while the U-shaped grooves 20 are opposed to each other. The first and second members 1a, 1b are fixedly fastened together by fastening bolts 2 and nuts 3 in the direction in which mating surfaces 5 are pressed together. Fastening force caused by the bolts 2 and the nuts 3 is depicted as circles 40 projected onto the mating surfaces 5 of the first and second members 1a, 1b. The bolts 2 and the nuts 3 are arranged such that lines of intersection (junction ridge lines) 6, each defined between a wall surface of the waveguide channel and the mating surface, are included in the respective projected circles 40.

Abstract: A method for producing grain-oriented electrical steel sheet having metallic luster and excellent punching property comprises the steps of decarbonization annealing a grain-oriented electrical steel sheet which has been cold rolled to a final thickness, coating the decarbonization-annealed sheet with an annealing separator consisting of magnesium blended with one or more salts of alkali metal or alkaline-earth metal, and finish annealing the coated sheet.

Abstract: In the production of a grain-oriented electrical steel sheet, a slab (1) is current-conduction heated, using the slab (1) as a resistor, under a condition of being on or below an apparent current density (I) of from 40 (A/cm.sup.2) to 0.5 P.sup.2 +100 (A/cm.sup.2), P being a pressure of electrodes in kg/cm.sup.2.