Metal flat washers, do you know the standard of surface grade [hardware]

Metal flat washers are divided into standard parts and non-standard parts. The standard parts have been modified from two to three surface quality levels:   Higher finishing surface (FB), the surface is allowed to have a small amount of defects that do not affect the formability and coating and plating adhesion, such as slight scratches and indentations , Pitting, roll printing and oxidation color, etc.  No matter how high the finishing surface (FC) is, the better side of the two sides has no obvious defects visible to the naked eye, and the other side must meet the requirements of FB at least.  Super high finishing surface (FD) The better side of the two sides of the product must not have any defects, that is, it cannot affect the appearance quality after painting or the appearance quality after electroplating, and the other side must meet the requirements of FB at least.  (3) The surface structure is modified from four to two, and the control value of surface roughness is increased. When the surface structure is pitted surface (D), the average roughness Ra is 0.6 μm.  (4) The regulations on Si and residual elements in the chemical composition of the five brands have been cancelled, and the content of C, S, Alt and other elements have been modified. Hardware, 15 years of craftsmanship focused on metal flat washers, 20,000+ sets of mold customization production experience, monthly processing of 100+ sets of molds, daily production capacity of 3 million punches, stamping accuracy up to 0.01mm, and 16 quality inspections. It can quickly solve time-critical problems for you, solve stamping accuracy problems, and solve production quality problems. Choose, choose to rest assured!