In the past, some casting experts believed that there were two pouring heads at the top of the Yongle Bell. In 1989, research personnel of our museum found a pouring head at each of the four joints between the handle and the body of the bell. The rain - type casting technique made it possible for the molten bronze to flow into the pouring heads evenly. So the shape of the bell was not damaged, blowholes and air holes were prevented effectively, and looseness of the internal structure of the bell was avoided. The Yongle Bell has been struck for more than 500 years, but it has never produced any unpleasant sound. This proves the compact structure of the cast.