These conflat demountable vacuum fittings have a flange size of ConFlat (CF) 1-1/3 inch with a glass viewport view diameter of .56 in and a glass thickness of 0.158". Demountable Viewports are used for ultra-high vacuum applications and molecular spectroscopy. These fittings use a Viton O-ring gasket, operate down to 10-8 torr (10-11 Pa), and have a max bakeout temperature of 150° C. The operable wavelength of the uncoated glass is between 350nm to 2100nm. This is a glass lens but other coated quartz fused silica is available. Fused silica is for all but the most demanding optical applications. They are preferred over glass viewports because of their transparency to UV ultraviolet radiation. We carry Uncoated and Coated UV viewports and replacement fused silica lenses. See middle graphic chart above for the different light transmissions for this glass lens. North American flange sizes are given by flange outer diameter in inches: 1-1/3 ("mini conflat"), 2¾, 4½, 6, 8, 10, 12, 13¼, 14 and 16½. In Europe and Asia, sizes are given by tube inner diameter in millimeters: DN16, DN40, DN63, DN100, DN160, DN200, DN250. These vacuum fittings are made of corrosive resistant stainless steel. At present we have the following demountable viewport sizes listed in the graphic below and have replacement viewport glass and O-rings for sale.