The strongest, most secure sanitary sight glass indicator available, Viewport’s mechanically prestressed windows are available in a sanitary clamp design for sight ports in processing applications or inline visual flow indicators. Unlike some other sight glasses, Viewport sight glasses meet the USP Type 1 standard for pharmaceutical use. Described as offering the optics of glass and the strength of steel, these glass elements provide a level of safety, and a useful service life, well beyond that provided by conventional tempered glass or plastic used as sight glass indicators. Even at the most extreme temperatures (as high as 536° F) or in overpressure situations, sudden, total failure – that involving leakage or explosive shattering of the glass – essentially never occurs. Viewport windows are formed by melting borosilicate glass into a precisely formed metal ring. As the glass cools, it solidifies, preventing the metal ring from contracting back to its theoretical size. The result is a uniform, mechanically prestressed fusion of glass and metal that combines excellent optical characteristics with greatly enhanced physical characteristics. A standout of sight glass indicators, the Viewport discs have an uninterrupted surface with no crevice to trap bacteria, epoxies, resins, or glue – a true fusion. The standard surface finish is 10 Ra μ-in (0.25 Ra μm). Electropolishing available upon request.