- Kodial 316LN DN38CF Viewport4 to 6 weeks delivery£0.00A zero length viewport has a thickness no larger than that of its mounting flange. This makes it easier to protect from accidental damage. It provides the best angle of view as there are no tubulation walls to restrict observation. Kodial viewports are offered in CF flange styles. The viewports comprise borosilicate glass optic which is sealed to a Kovar weld ring using an induction heater process. The optic assemblies are helium leak tested and cleaned for ultra high vacuum (UHV) conditions.