I believe what you have here are the Overlocking legs, actually. Would have to double check with either the Halo 4 assets release thread, or the game itself, but pretty sure that's what they are.
Edit: Ok, so it was bugging me more than it should that I didn't know what these were off the top of my head, so I fired up Halo 4 and took a look...and Demogorgon is right, these legs are NOT in the game, nor are they a close enough match to anything in the game to hazard a guess as to what they were to become.