This is a vintage 1940s sterling silver N.T.A. (North Trans Atlantic)TrainTrolley with moving wheels. This charm is marked STG for silver and JMF for J.M. Fisher Company of Attleboro, Mass. It measures 1/2" with the bail ring by 5/8" in length.
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Vintage Sterling JMF Articulated NTA TrainTrolley Caboose Charm 1940s