These conflat Viton gaskets fit a conflat flange size of 3.375 inches. They have been pre-baked and degassed to limit the outgassing in your vacuum system. They can also be used for testing and multiple times for assembly and disassembly. The knife edge of the CF flange presses against the Viton gasket but does not cut into it, making it reuseable, unlike the CF copper or silver gaskets that can only be used once. North American flange sizes are given by flange outer diameter in inches: 1.33" ("mini conflat"), 2.125", 2.75", 3.375", 4.50", 4.625", 6.00", 6.75", 8.00", 10.00", 12.00", 13.125", 14.00", and 16.50". In Europe and Asia, sizes are given by tube inner diameter in millimeters: DN16, DN40, DN63, DN100, DN160, DN200, DN250.