This is a wire brace for the Monoprice Select Mini heated bed. This is used when you re-route the bed wires out the back and is intended to provide support to the wires at the bed. This was designed so that you could install it after you've routed the wires, there's an opening in the support loop so you don't have to feed the wires through. The wires are then secured in place using a zip tie so it's easy to remove it for maintenance. The wire brace is held in place by the screws that hold the rods of the y-axis. I recommend installing this one screw at a time so the y-axis assembly stays relatively intact. I also used some wire bundle wrap, as seen in the photos, similar to the bundle that goes to the hotend. I found this at the hardware store and is the 3mm variety. This isn't necessary though, a few gently tightened zip ties along the bundle will do just fine.
Added a version with the wire brace centered.
Added a version with the wire brace on the left.