I think the differences between sus304 and 304 are:

1. The sources of materials are different. SUS304 is a Japanese JIS standard, and 304 is an international standard.

2. The chemical composition is slightly different. The nickel content of SUS304 is slightly higher than the international standard 304.

3. Steel grades are expressed in different ways. In Japanese standards, SUS represents stainless steel, while 304 is the name of the international standard.

4. The fields of use are slightly different. SUS304 is often used in chemical, energy and food fields. 304 is suitable for manufacturing various equipment and engineering structures, as well as kitchen appliances, etc.