Flame King Overfill Protection Valve helps prevent the 20LB propane tank overfills by closing when propane liquid level reaches to an 80% fill rate. Made of high quality premium materials for your safety - UL Listed. This valve is compatible only with the 20-Pound Horizontal and HOG Propane Tank Cylinders by Flame King - item #s YSN20HZL and YSN20HOG. Does NOT fit the vertical 20LB tank.