These brackets replace the lower Z-axis endstops and also include two additional M3 mounting holes with gusseting to affix to the rails by way of two additional T-nuts. This should serve to stiffen these joints and help prevent rail rotation.
The brackets also incorporate a plate to cover the Z-belt hole in the corplast for an improved aesthetic. There is a narrow slot in the cover portion to allow the Z-belts to slide in for post belt installation. The Z-belt hole cover should be in the proper location if everything is aligned well.
You can use the logo or nologo variety depending on your tastes. You will need two left and two right brackets to do all 4 corners.