23 INTERNAL AND EXTERNAL CYLINDRICAL GRINDING MACHINES, RADIUS GRINDING MACHINES (OSCILLATING GRINDERS), PISTON TURNING AND GRINDING MACHINES, PISTON TRUING MACHINES, VALVE SEAT CUTTERS, VALVE REFACING GRINDERS, VALVE SEAT GRINDERS, PORTABLE SURFACE POLISHING MACHINES, BORING MACHINE CUTTING TOOLS, REAMING MACHINES, CYLINDER BORING MACHINES AND ATTACHMENTS, BOLT EXTRACTORS, DRILLING ATTACHMENTS FOR MILLING MACHINES, AND VALVE SEAT BORING MACHINES