Train Tunnel Inc Retaining Walls. Four Track. N Gauge Model Railway scenery V2 This kit will arrive ready to assemble. I suggest using a little Pva craft glue to ensure a good bond. Specifications; Centre part overall measurement; 220mm x 55mm. This has an opening which measures 160mm X 40mm Retaining walls; 61mm x 51mm I can make custom orders. Please contact me for more details. Made from high quality 3.0mm thick Medite (laser quality MDF), plain finish ready to be painted and decorated. These item are laser cut, the laser cutting process produces a brown finish to the edges of the MDF. All laser processing marks can be easily removed by a light sanding or simply painting over.