O scale Single sliding shed door.
This is the type used on KHM's On30 Backwoods Roundhouse.
The door slides in a channel with simulated rollers.
The door is 3 1/4" tall x 2 1/4" wide (84 x 60mm), and the supporting track is 4 3/4" (120mm) long.
microply parts, peel and stick basswood framing with stencil card P&S window frames.
Both sides of the doors are detailed so it looks good inside and out.