FILTERS FOR GAS DEVELOPING MATERIALS AND FLUIDS - NAMELY, FOR AIR, GAS, FUELS, COMBUSTIBLE MATERIALS AND OILS, FILTER INSERTS, COMPRISING POROUS MATERIALS - NAMELY, PAPER, PULPBOARDS,[ ASBESTOS ], FELT, SILICEOUS, CERAMIC MATERIALS, AND METALLIC, NATURAL AND SYNTHETIC FIBER, WEBS, FABRICS AND KNITTINGS, AND THEIR PARTS