TEN-HIGH Diameter 18mm Focal Lens for CO2 Laser Cutting engraving machine, FL: 1.5" (1.5"/38.1mm) High Quality ZnSe Material. Excellent Optical Properties. Plano convex shape (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: 18mm(0.71 inch), Focal length: 38.1mm(1.5 inches), Thickness: approximate 2.2mm (0.09 inch)