23 MACHINE TOOLS USED PRINCIPALLY IN THE MACHINING OF METAL PARTS-NAMELY, FOR AUTOMATIC AND NON-AUTOMATIC INTERNAL GRINDING MACHINES, BOTH OF CHUCK TYPE AND OF CENTERLESS TYPE, ROTARY SURFACE GRINDING MACHINES, PRECISION BORING MACHINES USED ALSO FOR FACING AND TURNING OPERATIONS, TOOL SHARPENING MACHINES, AND FOR THE PARTS AND UNITS OF ALL SUCH MACHINES AND THE TOOLS, ATTACHMENTS, ACCESSORIES AND FIXTURES THEREOF, INCLUDING TOOL HEADS, WORKHEADS, CHUCKS AND THE LIKE