D-sub connectors were once widely used in RS-232C serial communication. Having this connector might be convenient for controlling old measuring instruments, etc. They have a trapezoidal shell with a mechanism to prevent incorrect mating, preventing reverse connections. Primarily used for RS-232C serial communication, connecting computers and peripherals, and as an interface for industrial equipment. D-sub connectors are still used in some industrial equipment today due to their diverse applications and high compatibility. This is a male/female set. I bought it a few years ago, but I probably haven't used it once. Male/female set, 9-pin. #connector #electronics