This is a pair of bridge support brackets that help stabilize the bridge over the finish line.  You must select the correct size (3.25", 3.5", 3.75", 4.0") of your track/finish line as well as the number of lanes you need these supports for. (3-4, 5-6, 7-8 lanes).  Current products are shipped with these already. Those who have older units may need to purchase these for upgrading their product's stability.