Abstract: Each end fitting of the union has an end for fixing the fluid line, and a coaxial metallic body terminating in an annular radial polished section where the internal bore of the union issues. A washer made of a deformable synthetic material is pressed on this metallic body and has a flat annular radial face which, together with the polished section, forms the free face for connecting the end fitting. A cylindrical metallic ring accommodates internally with a contact fit the two washers and a portion of the two metallic bodies, so that the two free connecting faces come to be opposite each other. Two clamping half-shells grip the two end fittings to ensure the connection of the fluid lines.