A simple 3D printed plastic tunnel for an O-scale train track.Variations: Straight variations are straight, and their length is the listed number.The curved variations list the degrees of a circle they cover.For example, 'O-36, 30 degrees' means that each piece covers 30 degrees of a circle, meaning that 3 of them make a 90 degree turn. The diameter of the circle that would be made by these pieces is 36'' (any curved track you purchase should have a listed diameter).22.5 degree variations mean that 4 of them make a 90 degree turn. 18 degree variations mean that 5 of them make a 90 degree turn. 15 degree variations mean that 6 of them make a 90 degree turn.Train not included. Tracks not included.3D printed pieces always come with some minor surface artifacts. You can cut away strings, and you can lightly sand the surface. But don't go too deep, because the outer shell is only about 1 mm thick.