This brass railroad caboose or car key is stamped MIRR and there are several railroads which used these symbols in the past. None is a large or well-known common line. The Minneapolis Industrial Railroad is one, the Mexican International Railroad and Michigan Industrial Railroad are two other possibilities. If anyone has a better ID on this let me know! This appears to be a scarce and very old key.
Caboose keys are far rarer than switch lock keys and the majority of them are not stamped with the railroad name. Keys from old or unusual lines can be very expensive. They have a rather unique size and shape (very long) and were made by a number of manufacturers who usually did not stamp their name on them, except for Adlake.
This large-top variety is 4-1/8" long and has a solid stem ending in a rounded point. One side is stamped "MIRR" and the other side is unstamped. The key is solid brass and heavy- weighing 1.4 ounces!
CONDITION-Fine. The key has not been cleaned and has a fine patina on it. It shows considerable usage wear and has a slight bend which may have been in the original cast piece. There is not other obvious damage.
I am offering several other marked and unmarked Caboose keys, all of which came from a Indiana estate collection with no additional information. If you buy several items from me I can combine shipping charges to save money- Ruby Lane cannot automatically do this, so wait until you get a combined invoice from me before paying.