... Lens 1), Brand: HENGXIANG 2), Material: Silicon 3), N=0.5 , B=40/20 , C=0.01 Flat-convex Silicon Lens1 ... ),Shape: concave, convex, flat, etc.4),Specification: Φ6-Φ22 5),Center thickness: 1.5-2.5mm6), Precision (the highest): N=2 , N=0 ... .5 , B=40/20 , C=0.01 7),Specification: In accordance ...