This is a set of windows at 4mm:1ft (OO-scale) for my Southern Diagramme 3105 plastic luggage van, British Rail PMV. You will need 8, so one is spare. I envisage fitting them into the window apertures on the body with the minimum of glue spotted around the edges, but check the fit first. The smooth surface faces outward, the grooves on the inside are to give the appearance of the wire rods behind the glass.