... engagement in R&D, manufacturing and international trade of precision steel tubes, and has more than 3500 tons ... to 18mm, of the precision ±0.03mm, and of inner surface roughness Ra0.4-0.6. The types of steel tubes ... include 10#, 20#, 35#, 45#, 160Mn, 20GrMo, 35GrMo, 40Gr. The products have the characteristics of small ... -Win businesses. DingRun High Quality Steel Hexagon Nuts