Those couplings are used for potable water, lavatory, air start, APU, engine oil and preconditioned air components.
Airbus Skydrol Service Coupling. Airbus Skydrol Service Coupling.
Boeing Skydrol Service Coupling. Boeing Skydrol Service Coupling.
CSD/APU Fill & Overfill Service Coupling CSD/APU Fill & Overfill Service Coupling