Surface treatment of Wood Screws: Most self-tapping screws are coated with zinc or zinc phosphate. Cadmium plating is rarely used because of its high cost and toxicity. If appearance is important, nickel or zinc plating can be selected. Chromium. Surface treatment will cause two problems: one is that surface treatment will not only increase the size (such as the reduction of holes, etc.), but also different surface treatments will affect the relationship between torque, tightening degree, and strength. When doing tapping experiments, different rules must be followed for galvanized, cadmium or phosphate treatment. When testing the applicable tapping diameter, the stainless steel screws used must be screws with the same surface treatment. Second, high hardness , Small-scale self-tapping screws often fail to use due to hydrogen embrittlement. In order to penetrate the iron plate, self-tapping screws have to be carburized. After carburization, high hardness and high carbon content will occur. In this case, hydrogen embrittlement will occur when electroplating or pickling treatment is performed. The method to eliminate hydrogen embrittlement proposed by the standard is: a). Bake within 1 hour after electroplating or pickling treatment. b). Temperature 375 ~ 425 oF (190 ~ 220 oC). Time at least 4 hours.