The plug brick is located at the lowest end of the plug rod and the refractory brick which is closely matched with the nozzle brick. When not pouring, it blocks the water inlet to ensure no steel leakage. When pouring, the plug bar shall be raised to make the gap between the plug brick and the nozzle brick, and the molten steel shall flow out of the nozzle. Control the height of plug rod and adjust the outflow of molten steel. The plug block and the core can be fixed by thread or pin. Plug brick can be clay, unburned high alumina and tar impregnated unburned high alumina brick.