Nate Nagel wrote:
> Does anyone have a link to any law or standard that allows or prohibits
> their use?
>

will you settle for proof (almost) by contradiction?;

http://standards.sae.org/j2879_201107/

indicates that SAE spec J2879 "applies to 90 degree double inverted
flares used on common sizes of automotive hydraulic brake tubes, and
their associated tube nuts and mating ports"

every test I've ever taken, had as the correct answer for brake line
repair, "use a double flare".

and that's enough for me,
GW