FD90 Series hydraulic quick-connect couplings are diagnostic couplings used to connect and disconnect pressure gauges to hydraulic systems. Coupling sets contain both a coupling body (female end) and a coupling plug (male end), eliminating the need for permanent diagnostic gauges. The automatic sleeve design allows one-handed connection. Flush-face valves provide minimal fluid loss and keep air from entering lines, while self-sealing valves connect and disconnect under pressure with minimal exposure to air or fluids.