Examining the train couplers is another simple way to identify the vintage of a Lionel product. Prior to World War II, the couplers were very toy like, hook shaped and had no resemblance to a full scale train. The cars were metal and had very colorful schematics. Post World War II trains more closely resembled full size rolling stock in color and used two different types of couplers. The entry level Scout series couplers do not open, are longer and resemble a capital "G." The more common couplers open and are compatible with modern O scale cars.

Lionel produced two types of electrical coupler. The early version, immediately post war, was operated by two extra rails either side of the middle rail. Each truck is in contact with these rails using contact shoes, and when a switch is thrown the power operates a solenoid in the coupler. The later type involved an inductive coil in the middle of the third rail reacting with a corresponding coil in the truck to provide electricity to the coupling. This was better than the first version since there were no contact shoes to get snagged with switch points."