These are 1/8" MDF pieces that serve as city block bases. These pieces bring the ground level up the level of the sidewalks on all of our 285th scale Modular Road pieces. See iamge with dimensions for sizes.
This kit is for those that want to make a 7.2" x 7.2" city block but want the base broken up into two 7.2" x 3.6" pieces. (see the images, I think it's pretty clear)