It's used in the 2017 Red And Blue Bumper Kit for the AM14U3.
Love the hex holes - once I figured them out
I'm using these to secure a bumper, but not in the way they were intended. I'm cutting off the flange (and a bit), putting a #10 hex nut in the hex holes, then securing the bracket to the inside of the chassis using another aluminum piece with a 1"x1" grid and #10 screws through the round holes. Then, secure the bumpers using #10 thumb screws which engage the captive hex nuts. The benefits of rivnuts, but they shouldn't start spinning after a few dozen uses.