These couplers are formed out of sheet metal, allowing the tab to mate with the slot of the coupler on the adjacent car. This design was simple and effective, and most makers of trains used some form of this design or another prior to World War II.

Marx made five different type of couplers between 1934 and 1974. If you’ve never seen Marx couplers explained before, here’s a primer on how to identify them and use them together. And I even have a few repair tips if you need them.

• In 2018, Solidworks added a “tab and slot” feature in the sheet metal menu. This allows the user to drastically speed up the process for the designer to add these features. Undoubtedly, this will lead to the proliferation of potential stress concentrations. Did We Forget About Stress Concentrations?
• There are specific sheet metal features you can use to create sheet metal bodies quickly. However, in some circumstances when the design requires certain types of geometry, you can use non-sheet metal feature tools, then insert bends or convert the part to sheet metal.
• Think about this for a while, and you can design a tapered tab that (when twisted with a pliers) will center the tabbed sheet in the slot and draw the slotted sheet down firmly to the tabbed edge. The welder then tacks the parts together, breaks off the tapered tab, and welds the parts together through the slot.

Tab and slot

You’ll see tab and slot couplers more often than any other type. Some people also call them hook and slot couplers, or simply hook couplers.

These couplers are formed out of sheet metal, allowing the tab to mate with the slot of the coupler on the adjacent car. This design was simple and effective, and most makers of trains used some form of this design or another prior to World War II.

Marx introduced this style of coupler in 1936 and continued to use it until the end in 1974, although Marx relegated it to locomotive-to-tender connections after 1972. Marx may or may not have used it longer than anyone else, but they were the last of the big-name train manufacturers to stop using it in the United States. It wasn’t very realistic, but it was inexpensive and effective. It’s also compatible with a number of other coupler types, so a Marx car outfitted with these couplers makes a useful transition car so you can run more than one type together.

Marx had some variants on this design. Cars intended for electric train sets had their couplers attached via a brass eyelet. Cars intended for clockwork-powered train sets had their couplers attached via tabs or a dimple that allowed them to slide. Clockwork locomotives like some slack in the couplers, as it makes it easier to get the train started. Electric sets work better without that much slack. The small amount of slack you get from fixed couplers is adequate for electric sets.

Sliding couplers can be prone to hanging up. Here’s my simple fix for that.

Compatible with: Joy Line (if height permits), plastic knuckle, plastic tilt.

Joy Line

Early Marx or Girard Model Works sets had a hook coupler with a round hole and a t-shaped hooked tab. Early American Flyer and Hafner trains used a similar design. It works the same way as the later tab and slot coupler and they will couple together if the height matches closely enough. This design lasted until 1935.

The later tab and slot design has less slack in it, which makes it more reliable. It is less likely to accidentally uncouple. The advantage to the earlier design is that it was easier for young children to use.

Compatible with: later tab and slot couplers and plastic knuckle couplers, if height permits

Tilt or fork

The tilt or fork coupler dates to 1942. Marx kept making it all the way to the end of its train production, in 1974. It was Marx’s top of the line coupler.

All of the train makers wanted a coupler design that could automatically couple or uncouple to improve play value. The tilt coupler was Marx’s second and more successful effort. Tilt couplers will automatically mate by running the cars into each other, as long as their height is close.

It’s a good idea to check your metal tilt couplers’ height against a plastic tilt coupler for smoother running. You can adjust the height slightly by gently bending the coupler up or down.

Later tilt couplers made of plastic had a slot in them to make them compatible with tab and slot couplers. When Jim and Debby Flynn licensed the name Marx Trains and started producing trains in the old Marx style, they included a slot in their metal coupler. Some hobbyists cut a slot in their metal couplers with a Dremel cut-off wheel so they can attach a tab and slot coupler to them. A small cut at the back of the existing opening suffices.

Both types of tilt couplers are completely compatible with one another.

If you ever need to remove or replace the spring in a tilt coupler, it can be difficult, but there’s a trick that makes it much easier.

Compatible with: Tab in slot couplers (plastic tilt couplers only)

Knuckle

After World War II, both Lionel and American Flyer introduced knuckle couplers, which look more like the couplers on real trains. Marx followed suit, although the Marx knuckle coupler is a single piece of plastic that doesn’t operate automatically. The Marx knuckle also won’t couple with Lionel knuckle couplers, but the Marx design is compatible with its tab and slot couplers. The tab fits securely enough into the knuckle that the two will stay together.

You can’t connect a Marx tilt coupler with a knuckle coupler directly, but you can connect a car with tab and slot couplers between the two in order to run all three together. Marx did a good job of keeping its various coupler types compatible with each other.

Marx made knuckle couplers from 1953 to 1974. Sometimes people refer to these as PKC, which stands for plastic knuckle coupler. Marx used the PKCs in its less expensive sets.

Now for some trivia: Scientific Toys makes a plastic train under the Eztec brand that somewhat resembles Marx’s least expensive plastic trains. Its coupler happens to be compatible with both Marx and Lionel knuckle couplers, though it won’t couple with a Marx tab and slot coupler. Installing an Eztec knuckle coupler on a Marx car increases its versatility.

Compatible with: tab in slot couplers

One-way

Marx’s one-way couplers are ugly but functional. One coupler is a simple post, and the other coupler is a pincher or claw that tightly grabs the adjacent post. If you turn a car around, it won’t connect, unlike other Marx designs. That’s why they call them a one-way coupler. This makes operations with this type of coupler difficult, since you have to be careful which way each car is facing, unlike real railroads, and unlike most competing designs.

Their design allows for automatic operation and they are very reliable. , but they were expensive to make because they had so many intricate parts. Assembling and installing them was very labor intensive. They also weren’t compatible with anything else Marx made. Furthermore, if a curious child took one of these couplers apart, it’s entirely possible a parent wouldn’t be able to figure out how to put it back together.

Sheet Metal And Tab Slot Design Guide

Another drawback with these couplers is that once they rust, they can stop working. A little bit of oil usually frees up the pincher fairly quickly.

Sheet Metal Tab And Slot Design Guide

This coupler isn’t very popular, even today. I think it’s more reliable than the fork coupler, but the fork coupler is more subtle. Subtlety is a virtue when it comes to couplers, so it was the more enduring of the two designs. Marx only made these from 1938 to 1942.

I frequently find cars with broken one-way couplers. Here are some tips for fixing them.

Conversion cars

When you have cars with incompatible coupler types, pick up a couple of beater cars with different types of couplers and swap them around. I’ve done this with several types of couplers so I can combine almost any make of train car I want.

Tab And Slot Sheet Metal Designs

Here’s my early approach with a Marx-Lionel conversion car, and a later effort for some cars that can convert between multiple types.