This is a support and wall bracket intended for IKEA SKADIS. They have the same dimensions as the original ones from IKEA and can either be screwed on (hole in the middle) or "twist-fit" - no screw needed.
Supports the center when heavier objects are added to the board (this caused mine to bend a bit).
It takes up 1 slot on the board. IKEA only provides 2 supports + metal rod, so this is a good addition to support the board.
It can also be used to mount cutouts on the wall.