For indoor use only. Radius Design Changeable Letterboards feature sturdy aluminum frames with rich powder-coated finishes, and lockable doors to protect your most important messages. For a contemporary interior, choose our ?Radius Design? Enclosed Letter Boards. Frames are fashioned of extruded aluminum with an attractive and long lasting powder coated finish. Standard features include: Acrylic safety glass windows, continuous hinges, concealed mounting brackets and locking doors. Includes a set of 165 count - 3/4" Helvetica letters.