Specification of our Rhombohedral prism as follow: *Material BK7 Grade A optical glass *Dimension Tolerance +/-0.2mm *Beam Deviation Up to 30 arc seconds *Angle Tolerance Up to 5 arc seconds *Flatness Up to λ/4 @633nm *Surface Quality 60/40 scratch and dig *Chamfer 0.3mm+/-0.1mm *Coating AR coating available Rhombic Prisms are used to display a beam laterally without changing it is direction. They maybe coated to transmit part of the beam and produce two parallel and displaced emerging beams. Can be coated to produce a polarizing beam separator. Dimension and coating may be available by custom orders.