TEN-HIGH Diameter 20mm Focal Lens for CO2 Laser Cutting engraving machine, FL: 2.5" (2.5"/63.5mm) High Quality ZnSe Material. Excellent Optical Properties. Meniscus (Convex-concave) lens for better quality when engraving. Superb Coating Process: Double-sided Solid Coating. Wiping Resistance. Long Working Life. High Precision Process: Excellent Substrate. Precision Slicing, Polishing, Grinding Processes. High Temperature, Laser Resistance. High Transmittance: High Quality Material and Exquisite Coating. Reduce the Loss of Laser. Higher Work Efficiency. Diameter: 20mm(0.79 inch), Focal length: 63.5mm(2.5 inches), Thickness: approximate 2.2mm (0.09 inch)