There have been three major types of Lionel knuckle couplers produced since resuming train production in 1946. Lionel knew it would have to make a splash when it brought its trains back after the end of the War, and the knuckle coupler was one of the keys.
Two of these coupler types are compatible with one another, but one has a gotcha.
Lionel’s standard knuckle coupler
The first, most popular, and most enduring type is the standard knuckle coupler. Through all the bankruptcies and changes of ownership, this coupler remained constant. The biggest advantage of these couplers was the ability to operate them remotely. Early models used electromagnets to open and close them for operation. Later versions use a device that resembles a thumbtack. This coupler was introduced in 1946 and widely envied, but patents generally prevented copying until the 1970s and 1980s. Sakai did copy it, and seemed to get away with it. Once it became evident that competing with Lionel was possible, its competitors cloned it widely.
Lionel’s dummy coupler
Lionel had to keep from pricing itself out of the market. That was the goal of the so-called dummy coupler. It was the same shape as the standard coupler and completely compatible with it, but unlike the costlier standard coupler, it didn’t operate. It was molded from a single, solid piece of plastic. The standard coupler provided better play value, but the dummy coupler allowed Lionel to sell cheaper sets and consumers could still use those trains with nicer, costlier trains with standard couplers if they upgraded. Lionel sold a lot of trains with these couplers from the 1960s to the 1980s.
Marx didn’t dare clone the operating knuckle coupler in the 1950s, but it did sell a dummy coupler adapter that could allow its diesel locomotives to pull Lionel cars.
Lionel’s Scout coupler
Last and least is the ill-fated Scout coupler. It was only made for a few years from 1947 to 1953. The design was clever in that it still allowed for remote uncoupling while being cheaper to produce than the standard coupler. The problem was it wasn’t compatible. That meant purchasers of those early Scout sets who later upgraded had to improvise with bits of wire, or cut off the Scout knuckles and install a 480-25 conversion assembly to run their old trains with their new ones. It was also less realistic. While Lionel’s standard knuckle coupler was much larger than scale-sized, the Scout coupler was even more so.
If you want to run Scout and standard postwar Lionel cars together, get a cheap Scout car and remove one coupler, then put a Lionel 480-25 on that truck. Couple your Scout cars on one side of the conversion car and the standard cars on the other.