SHEET METAL PIPES, ELBOWS, DUCTS AND FITTINGS FOR RESIDENTIAL HEATING, COLLING AND VENTILATING SYSTEMS; STEEL REGISTERS; CAST IRON AND SHEET METAL DAMPERS AND DAMPER REGULATOR SETS; SHEET IRON AND STEEL ACCESSORIES FOR ABOVE SYSTEMS-NAMELY, ROUND, CIRCULAR AND RECTANGULAR STEEL PIPES AND DUCTS FOR THE TRANSMISSION OF WARM AND COLD AIR, BOOTS, ELBOWS, ANGLES, CHIMNEY HOODS, REGISTER BOXES, GAS VENTS, PIPE FITTINGS AND DAMPERS