SHINA New ZnSe Focal Lens for CO2 Laser Cutting Diam 20mm FL:1" 1.5" 2" 2.5" 3" 4" (1"/25.4mm) Mateial: Znse Diameter: 20mm Focal length: 1''/25.4mm, 1.5''/38.1mm, 2''/50.8mm, 2.5''/63.5'', 3''/76.2mm, 4''/101.6mm Thickness:approximate 2mm Edge thickness variation (ETV):&lt;= 0.002''