Corner Cube Prism has the property that any incident beam will be reflected parallel to itself, regardless of the incident angle. These prisms are ideal where precision alignment is difficult or time-consuming. Material:N-BK7 H-K9L JGS1 Size:12.7mm 25.4mm 38.1mm 50.8mm or customized size Beam Deviation:+/-3'' +/-5'' +/-8'' Flatness:1/10lambda at 632.8nm Surface Quality:40-20. Clear Aperture>90%