23 MACHINERY BEARINGS, BUSHINGS FOR MECHANICAL WORKING JOINTS AND MACHINE PARTS INCLUDING PISTONS, VALVE STEM GUIDES, POROUS BRONZE PLUGS, TOGGLE PINS, FILTER ELEMENTS, SLIDES, GEARS, POROUS BRONZE RINGS , END PLATES, THRUST WASHERS, POROUS BRONZE RETAINERS, AND SIMILAR PARTS OF POROUS BRONZE FOR BEARING SURFACES.