The tiniest way to identify tin cans is to look at the appearance of the cans: first, to see if the cans are rusted, if the labels are contaminated, and then see if the bottom lid is complete, slightly concave inwards, and not bulging. Both are normal. In addition, you can gently tap the lid to listen to its sound, normal cans sound crisp, if the sound of flapping, it may leak. In addition to the methods described above, glass jars can be used as well as canned fruit, etc. In addition to the above methods, the factory generally uses a type of anti-theft cap. The center of the normal can lid is concave. If the can has been opened or leaked, the bottle cap The center is raised outwards and cannot be restored.