Because the plating layer has a certain thickness, after the surface treatment of the part, it will inevitably cause the change of the size of the part. Generally, the dimensions and tolerances of the parts specified on the design drawings refer to the final dimensions and tolerances of the parts. If the parts do not have matching requirements, electroplating or electroless plating is still feasible on the final dimensions of the parts; if the parts have higher precision, The fit gap after assembly cannot accommodate the thickness of the plating layer and its deviation relatively, so plating on the final size of the part is detrimental to the assembly and working performance of the product. In order to solve the problem of size matching of parts with matching requirements after plating, it is necessary to negotiate with the design and process departments of the parts to determine the pre-plating process dimensions of the parts, and reserve the thickness of the plating layer and the size deviation of the plating in advance. It must be noted that it is not feasible to reserve the thickness of the plating layer and not reserve the thickness deviation that may occur during plating.