Din 7504. Material : low carbon steel, stainless steel(A2/A4). Material : Low carbon steel ,stainless steel (A2/A4),Brass. Surface : zinc plated(Cr6/Cr3), yellow zinc plated, black oxide, black zinc plated, hot dip galvanization decromate, ruspert, Drill hole, forms mating thread and cooperation. No more need for difficult alignment of two or elements.