Thank youAll previous ATF classifications involving stabilizing brace attachments for firearms are superseded by the Jan 31st ruling and are no longer valid. So basically, no, there isn't a specific brace that is currently legal to use across the board. The only way to find out if a configuration you have in mind is legal would be to submit it to the ATF (good luck with that). In general, if a brace makes it at all possible to shoulder the firearm, then it wouldn't likely be considered legal.