In the October Model Railroader I noted couplers with "upper shelf (Kadee) and "lower shelf " (McHenry). Can someone tell me what this means?
These are to duplicate Type F couplers. The shelf (which is a protrusion above or below the knuckle) is used to prevent one car from riding up and puncturing another in teh event of a collision. Not surprisingly these are found mostly on Tank cars (Although some passenger couplers are quite similar and these may be used to substitute).
Lower shelf couplers protect the other car, while upper shelf couplers protect the car they’re mounted on.