"At this time, the metal materials in the claim can include other metal materials with the same function besides iron, copper, aluminum and stainless steel, but it will never be understood as including all metal materials, even including metal materials such as sodium and gold." —————————— Here is a key word, that is, it can achieve equivalent effect. As transmission parts, the properties of hard metals are used, but sodium and metals are soft metals and cannot be used to manufacture transmission parts, so they cannot be included. If the claim is written like this, "the examiner thinks that there are one or more sub-optimal features that cannot achieve the relevant technical effects, then it is determined that the claim cannot be supported by the specification", and the conclusion is this.