Nothing compares to the flexibility, durability and savings of the Duo-Flip system. In moments, you can have any possible combination of ID numbers, then flip to display the corresponding placard. Self-contained placards easily fold over four aluminum hinges. Four stainless steel fasteners lock your chosen combination securely in place. Standard Duo-Flip systems contain three or more panels in one frame. The unique deep-formed aluminum frame provides maximum wind protection and stability. Duo-Flip is approved for use by private and fleet carriers.