These Replacement O-Rings follow International Standards Organization (ISO) standards and have a flange size of NW-63. ISO flanged vacuum fittings are commonly used to build process vacuum plumbing and systems for industrial applications. The fittings are quick to assemble using double claw clamps and a centering ring. The ISO standard sizes for LF NW ISO large flanges are NW-63, NW-80, NW-100, NW-160, NW-200, NW-250, NW-320, NW-400, NW-500, NW-630.

They are made of. is well known for its excellent resistance to heat (400°F/200°C) and to aggressive fuels and chemicals. 

O-Ring Viton, for NW-63 Centering Ring, 

ISO-LF Flange Size: NW-63

Common Dimensions: ID = 2.85" (72mm)