Abstract: A tubular body has rectangular-shaped slot formed in the top portion thereof, and matched eccentric convex protrusions are formed on both sides of the body. A core is provided with a concave-shaped groove on its surface that is matched with the slot, when the core is inserted into the body. A cable is connected to the core. A rear cup is tightly fitted to the rear end of the body for securing the cable that is disposed externally through the hole. An insulation shell is tightly shielded on the outer rim of the rear cup and has an enclosed protrusion stopper. A locking device is provided which mates with the slot of the body. The locking device is furnished with ring-shaped side wings that ride on the body and touch the protrusions which serve as a force-receiving point. A coil spring is inserted from the rear end of the body and is located in between the locking wings and the rear cup. A slider is provided which can accommodate the locking wings of the device.