This is an HO scale flat car model of the Southern Pacific Railroad's first steel flatcar, designed around 1903. The CS-35 was a 36 foot long flatcar, built out of fabricated steel shapes. The SP designed both this car and the CS-35A 40' car at the same time in a flat car bake-off. The 40 foot car won. None of this CS-35A cars were ever built.
On a good resin printer, this model is approaching the quality of injection molded plastic.