[ GAS DISTRIBUTION APPARATUS; FLUID FUEL BURNERS FOR INDUSTRIAL USES AND PARTS THEREFOR; ] INDUSTRIAL HEATING EQUIPMENT ELEMENTS USING GASEOUS FUEL -NAMELY, FURNACES, KILNS, OVENS, DRYERS, LEHRS, AND HEAT TREATING MACHINES FOR USE IN HEATING METAL BODIES, FOR HARDENING AND ANNEALING PURPOSES AND PREPARATORY TO FORGING AND OTHER METAL WORKING OPERATIONS, AND PARTS OF SAID ELEMENTS