This series of circular electrical connectors is the metric series among the three, featuring the same number of cores, slightly larger shell diameter for easier cable welding. The socket mounting options include bowl-style, nut-tightened, and wall-through. They are locked securely with the plug's screw-type locking and further secured with three locking pins, ensuring a waterproof seal and vibration resistance to prevent loosening. Generally used for outdoor equipment, communication signal connection systems, computer systems, postal and railway command systems, and the connection of electrical and telecommunication signals for imported medical equipment and devices.