AWS A5.8 PDF

This specification prescribes requirements for the classification of filler metals for brazing and braze welding. It includes filler metals for brazing with or without a flux, and in all protective atmospheres, for various applications, including those for vacuum service.(Footnote 1) Filler metals identified by the prefix "RB" indicate that the filler metal is suitable for use both as brazing rod for braze welding and as a brazing filler metal.

Footnote 1 - Filler metals for vacuum service are for devices operating in a vacuum, regardless of the atmosphere used in making the joint.