These dual sides are made of MDF to provide a cost-effective alternative to Walnut. MDF is Medium Density Fiberboard. It's pressed wood particles and resin. MDF is very straight and has good strength. These sides are the same shape as a pair of straight sides and a pair of angled sides put together. Can be used in two different orientations. Mount to two Box11 frames for 22-spaces total, or use the connecting bracket (see below) with four Box11 frames for 44-spaces total. Screws included. Unfinished - sand and paint as you wish.