Old wagon grain boards. They would put on top of grain wagons for more capacity. I had them in a shed when I purchased the house. Probably 60-70’s green painted original. I cleaned stained and waxed. Used copper nails and some black hardware I had. I am including Velcro 5 pound per times 4 to mount but that’s up to your. I didn’t want to use new screws. I have old nails and screws and if you prefer just ask. I love the contrast of the old with the new.