Looks like a valve handle , not a wrench. It's long for leverage. The hole at the end is to lock it into position, the smaller hole probably had a pin on a chain attached to it.
@Azlotto The square hole is the giveaway, most nuts have six sides but valve stems are square or round as a rule.. My guess would be that it controlled an air pressure line or hydrologics .. such valves would be common on trains of all types as well as the rail cars.
