The circular connector has the advantages of low contact resistance, long endurance and reliable contactuality, whose socket is covered with guide stainless sleeve. Its technical index conforms to TB/T2716-1996 of Chinese Railway Department. The boyonet socket joint is adopted between plug and receptacle. Due to convinient joint and easy preformance, it is widely used for the connection of electronic equipment on the train and electronic joint. The plug and receptacle can be mounted with pins or sockets.