B16.5 has 3 material groups. Groups 1, 2, and 3. Each group has sub groups. Groups 1.1, 1.2, ..., 2.1, 2.2, ..., 3.1, 3.2, ..., etc. Each of these subgroups have different pressure / temperature ratings.
Hint: class 150, 300, 400, 600, 900, 1500, and 2500 are identifications not actual...