ASTM stands for American Society for Testing and Materials.
These standards specify the chemical composition, strength, testing, product
form and dimensional tolerances of different material products. Materials are
listed by a 3 digit number with letter prefix (E.g., A105 specifies carbon
steel forgings for piping applications. This is a common material used for
flanges)
These are below mention codes
A. The American Petroleum institute (API).
B. The American Iron & Steel institute (AISI).
C. The American Society for Testing and materials (ASTM).
D. The American National standard institute (AISI).
E. The American welding society (AWS).
F. The American Water Works Association (AWWA).
G. The American Society for Mechanical Engineers (ASME)