The Vintage Lionel Big “O” Size Extension Bridge 6-2122 is a classic model train accessory designed for model railroads. Manufactured by Lionel, this extension bridge is specifically made to expand the layout of a Lionel Big “O” size train system. The model number 6-2122 indicates the specific design and compatibility with other Lionel products. This accessory allows enthusiasts to create a more intricate and realistic train layout, adding an additional element of fun and creativity to model railroad building.