23 MACHINE TOOLS USED PRINCIPALLY IN THE MACHINING OF METAL PARTS-NAMELY, FOR AUTOMATIC AND NON-AUTOMATIC INTERNAL GRINDING MACHINES, CENTERLESS INTERNAL GRINDING MACHINES, ROTARY SURFACE GRINDING MACHINES, PRECISION BORING MACHINES USED ALSO FOR FACING AND TURNING OPERATIONS, TOOL SHARPENING MACHINES, AND FOR THE PARTS OF ALL SUCH MACHINES