A coupling device comprises a cylindrical, hollow casing or body to be permanently connected to a conduit for pressurized air; The casing is provided with a follower nut, which is threaded onto the casing and permits the insertion of two interior gaskets and an intermediate, metallic sleeve radially between the inside of the casing and the outside of the end of a pipe section fitted into the casing; Each gasket is of a standard cylindrical dimension and is formed of resilient material such as rubber or a rubber-like composition, whereas the intermediate sleeve is provided with external and internal recesses or shoulders for receiving each of the gaskets and preventing axial displacement of the latter, when the follower nut is screwed onto the casing; Moreover, the radial dimensions of the intermediate sleeve are chosen in view of the difference between the internal diameter of the casing and the external diameter of the pipe section to be coupled thereto; Thus, upon connection, the joint will be air tight; Moreover, standard casings and standard gaskets can be used together with radially different intermediate sleves for connecting pipe sections of different diameters