DUCTS MADE WHOLLY OR PRINCIPALLY OF METAL FOR TRUNKING PIPES AND CONDUITS FOR GASES OR LIQUIDS; PIPE FITTINGS, FASTENERS AND FASTENING DEVICES, NAMELY, BOLTS, NUTS, RIVETS, SCREWS, WASHERS, PLUGS, CLIPS, CLAMPS, MOUNTING PIECES, BRACKETS AND BANDS, ALL OF METAL AND ALL FOR DUCTS FOR TRUNKING PIPES OR CONDUITS FOR GASES OR LIQUIDS