A Ruby Filter, is a small device that you look through to aid in the identification of gemstones, in particular to spot real rubies amongst gemstones that are not rubies, or vice versa. Specifications: Filter Diameter: 20mm Body: Made of heavy metal Lens: Advanced Optic Glass, the retail stores sell this level of lens for twice of our price. Brand new, ships in 1 business day. Additional Details ------------------------------ Package quantity: 1