You are referring to "furnace brazing" which is different than "fillet
brazing" (also known as braze welding)

see:http://www.henryjames.com/gasf.html
I believe they are generally a nickel silver braze.
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Roger that. The original post had to do with bicycles, several
manufacturers of which use that method for fabricating the frames.

-R.S.Hoover