As sockets and plugs are affected in the circumstances (such as humidity, dust), the contact resistance between the sockets and plugs would change greatly, which affect the performance of electrical transmission directly. Therefore the designation for the contact structures of the sockets and plugs is very important, in particular for the sockets and plugs used in the explosive atmosphere. The principle of self-cleaning contact joints has been adopted when designing for the sockets and plugs all the time. The main part on the joint of inserting sleeve in the socket is an elastic shutter type spring casing which has many joints, which ensure low contact resistance and low temperature rise, while reducing the force of inserting and pulling. It is shutter type spring casing designed that ensure the correct function and self cleaning effect. Therefore, connecting the inserting sleeve with shutter type spring casing almost need not maintain. The sockets and plugs are designed to be used in bad environments. The degree of protection can be ensured because of using the protective cover. Features: 1) Self-cleaning inserting sleeve, low transmission resistance 2) Protective covers ensure high degree of protection 3) Small force of inserting and pulling