These are double sided anti-reflection coated focusing lenses for 10.6uM laser engravers and cutters. The material is Zinc Selenide ZnSe and the lens is positive meniscus, they have a focal length of 50.8mm or 2 inches which is generally the standard focal length on most Chinese economy laser cutters from 30W to 80W.
They differ from more expensive lenses in that they are unbranded and made in China.
They are packed in a hard case and include a lens cleaning cloth.
The item is supplied with free shipping in the UK.