That kind of joint requires hours of work with emery cloth.
Doubt you could get a fillet to be that small and still maintain strength, throat thickness must be tiny.
Looks more like super neat tig, any examples of TIG NJS?
but you cant see any welds, tig is tig.. hmm
Have you seen Ricky Feather's stuff?
@IR started
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That kind of joint requires hours of work with emery cloth.