Using finished pipes of DIN high-precision cold-drawn bright seamless steel tubes as the base for phosphating, the inner and outer walls of the steel tubes are treated with imported environmentally friendly phosphating solution to form a black phosphating protective film. The micro-pores in the phosphating film absorb anti-rust oil for rust prevention, and both ends are sealed with caps for dust protection. Main features: The steel tubes exhibit a shiny black color, with no oxidation layer on the inner or outer walls. They can withstand high pressure, are leak-proof, highly precise, and possess a high surface finish. They remain deformation-free under cold bending, and do not crack during flaring or flattening. With surface anti-rust treatment, these tubes are widely used in hydraulic systems, serving as high-precision seamless steel tubes in hydraulic systems, oil presses, injection molding machines, and various engineering machinery hydraulic systems.