There are precision casting and ordinary casting for grooved pipe fittings. The quality of the surface of the precision casting should be treated by chemical methods, and the quality is related to the ratio of the reagents. For ordinary casting, I know there are two kinds of surface coating: spray painting and powder coating. After all, it is a casting, and the surface will not be treated. The surface quality after painting is still not very satisfactory. After powder coating, the surface is very good. Tested with a thickness gauge.