The ASTM specification, the grade identification symbol (letters and numbers), and the melt number or melt identification.
Material — plate and forged flanges, and flanged fittings
4.2.2(b)
The ASTM specification number and the grade identification symbol.
Optional trade designation
4.2.2(c)
The manufacturer may add its trade designation for the material grade, provided confusion of symbols is avoided.
Pressure class
4.2.3
The number of the rating class designation: 150, 300, 400, 600, 900, 1500 or 2500.
Conformance mark
4.2.4
The designation "B16" or "B16.5", preferably next to the class designation. An "ASME" prefix is optional.
Size
4.2.6
The NPS designation. Reducing flanges and reducing flanged fittings carry the applicable NPS designation for each opening (paras. 3.2 and 3.3).
Ring-joint flanges
4.2.7
On the edge (periphery): the letter R and the corresponding ring-groove number.
Multiple material marking
4.2.8
Optional: more than one applicable specification or grade symbol, placed to avoid confusion and following ASME BPVC Section II, Part D, Mandatory Appendix 7.
Case number
4.2.9
"Case ##" when the flange or flanged fitting relies on and meets the requirements of a Case.
Temperature (optional)
4.2.5
Not required. If the temperature is marked, it must be shown with its corresponding tabulated pressure rating for the material.