BK Square Windows Lenses:
Material:BK7 grade A optical glass Length:+-0.1mm
Width:+-0.1mm
Center Thickness(TC):+-0.2mm
Surface Quality:60-40 scratch-dig
Surface Flatness:1/10 wave @632.8or 1/10 wave @632.8 each inch
Paralleelism:1 arcmin
Clear Aperture:90% of diameter
All dimentions are in millimeters.