Guillemin couplings are also called AFNOR fire couplings. They have the characteristic of being symmetrical; the two elements to be engaged together are placed opposite each other. A perfect seal is generated with a twisting movement in opposite directions by making half a turn of the rotating ring nut of each in the guide of the other. The coupling is done by hand, but then it is necessary to use the appropriate tool to tighten the connection well. The Guillemin symmetrical coupling (AFNOR) is widely used in brass, aluminium and stainless steel. The coupling is available in the following variants: symmetrical coupling with female thread and coupling collar, symmetrical coupling with male thread, hose connector with coupling collar and cap.