THE KNUCKLE, OUR PART NUMBER KN-1, PROVIDES A METHOD FOR MOUNTING THE CMM CALIBRATION SPHERE. IT IS MACHINED WITH A CLEARANCE HOLE FOR AN M10 OR 3/8" HEX HEAD CAP SCREW. IT IS A MADE FROM A SPHERE WITH A FLAT AT 90 DEGREES AND A FLAT AT 45 DEGREES. THERE IS AN M10 X 1.5 THREADED HOLE IN THE CENTER OF EACH FLAT. IT CAN BE MOUNTED DIRECTLY ON THE CMM TABLE, OR IT CAN BE MOUNTED ON TOP OF ANY LENGTH OF OUR STANDARD EXTENSION ( RISER ).