Depending on actual conditions for pouring steel, the preheat type and non-preheat type can be selected for long shround(LS), and stopper can be different in material and structures, according to different steel grades and steel pouring duration. Submerged entry nozzles(SEN) of different shapes, different materials and different structures can be selected according to different types of continuous casting machines, different  cross-section billets and slabs being cast and different pouring duration. The purpose is to increase service life and ensure quality of liquid steel .