1. Fittings and flanges

The difference in terminology between flanges and fittings is not well defined. The term "fittings" is generally reserved for assemblies connecting two pipes with diameters under 80 mm, and "flanges" for larger diameters. In principle, a fitting comprises the flanges and the gasket.

There's no limit to the dimensions of these fittings; in fact, manufacturers and users have been unable to agree on a general standard that would cover all pressure ranges [1] . There are, however, a few standards that are the result of efforts undertaken in the sixties: a type of quick coupling (based on a model registered by Leybold) has been standardized for diameters under 50 mm, and is often referred to as a Pneurop coupling, after the first standardizers. For larger diameters, in the absence of agreement on the tube...