Vortex Optics Viper Riflescopes Single-Piece Tube Maximizes alignment for improved accuracy and optimum visual performance, as well as ensures strength and waterproofness. Aircraft-Grade Aluminum Constructed from a solid block of aircraft-grade aluminum for strength and rigidity. Waterproof O-ring seals prevent moisture, dust and debris from penetrating the riflescope for reliable performance in all environments. Fogproof Argon gas purging prevents internal fogging over a wide range of temperatures.