Abstract: A fitting to be secured on pipes can be used with a number of distinct pipe materials and types. The fitting includes a nut receiving a Belleville spring washer. As the nut is tightened on threads on an end fitting, it forces the Belleville spring washer away from a relaxed position. This causes a radially inner portion of said spring washer to dig into an outer surface of the pipe, locking the Belleville spring washer, and hence the nut, on the pipe. The deformation of the washer also forces a ring against an inner seal, deforming the seal against the pipe, the nut, and the end fitting. In a second embodiment, a second washer is also deformed. The present invention provides a simple and universal method of attaching pipes to end fittings.