Casing pipe with a total of H40, J55, K55, M65, N80, L80, C90, T95, C95, P110, Q125 more than twenty different steel grade and type. In order to distinguish between different grade of steel strength, thread type, respectively, with different color code and symbols represent represent steel grade and thread.

Color label and english letters at the back of the 2 or 3 digits said the minimum yield strength steel grade oil casing, such as J55 said its minimum yield strength of 55000 pounds per inch (379 mpa) up to 80000 pounds per inch (552 mpa), 2 P110 minimum yield strength of 110000 pounds per inch (758 mpa) up to 140000 pounds per inch 2 (965 mpa).H, J, K, N for general strength oil bushing, C, L, M, T for qualified yield strength oil bushing, which has certain anti-sulfur corrosion resistance.