This is the REVO® OFA Optical Flat Artefact #A-5764-3142. The OFA optical flat artefact is used as a check on the suitability of a CMM for surface roughness measurement.  It comprises six optical flats mounted in the faces of the cube and can also accommodate two SFAH artefact holders.  The OFA can be secured to the bed of the CMM where required using the adaptors supplied.