Mesh, is the number of holes, that is, the number of holes per square inch. The larger the mesh size, the smaller the pore size, the higher the fineness of the powder. In general, mesh X pore size (microns) = 15,000. For example, 400 mesh is about 38 microns; 500 mesh is about 30 microns. Due to the problem of opening rate, that is, because of the different thickness of the wire used for braiding, the standards of different countries are different. At present, there are three kinds: American standards, British standards and Japanese standards. Among them, similarities between Britain and the United States and Japan are more. Our country uses the American standard, that is, it can be calculated by the formula given above.