This is a set of four steps (enough for 2 locomotives), as used on the running boards of some steam locomotives. They are patterned after those used on Southern Ry. and the Danville & Western Ry., with specific details based on photos of Southern Ry. #154 during restoration.
While similar to the plastic versions I have in my shop, this set is specificaly designed to be printed in brass, with slightly modified hole diameters and positions to suit the material.