The Dr. Bag Stabilizer is for rear bags that need stability or added height it is designed to be used by sitting the rear bag directly on top. The outer edges are sewn and filled with sand to help stabilize the bottom of the bag or level out an uneven surface. Makes your bag rock solid.Stabilizer for standard bottom Measures Approx.: 8-1/2" L x 6-1/2" W x 1/2" Tall.Comes pre-filled with sand due to difficulty of filling.