#4 finish is one of the many generally accepted, mechanical finishes which are often used in the metal finishing industry. Both the NiDi No. 9012 and previous revisions of ASME BPE specifications include a list that describes various mechanical surface finishes for stainless steel. A few common finishes include:
#4 - A widely used, general purpose finish produced by finishing with a 120-150 mesh abrasive. This finish is commonly found on architectural panels and stainless steel kitchen appliances and sinks.
#2B - A bright, cold-rolled finish. This finish is a standard finish for raw sheet metal and is produced at the mill.
#8 - A highly polished, highly reflective, "mirror like" surface . This finish is produced by polishing with successively finer abrasives followed with extensive buffing.