Couplers Vs. Couplers
There are a number of coupler choices available for the HO modeller. So, it might be worth while to look at some of the pros and cons of some of the various types. The title photo shows three of the most common. On the Left is the McHenry in the center is the Kadee "Standard Head" and on the right is one of the Kadee Hon3 #714 couplers.
The differences between each of these couplers can easily be seen at this angle. The Kadee "Scale head" on the left, McHenry center and Kadee #714 on the right.
All of the couplers here are made to replicate prototype couplers and all are designed for automatic coupling and magnetic uncoupling using either a magnet between or under the rails. I chose not to avail myself of the magnetic uncoupling feature as the trip pin is unsightly and my railroad is small enough to allow for uncoupling with the use of a pick (I use a shish-ka-bob skewer)...but that is another story. Further, it is necessary to note that any of these types may be used together with any of the other as they are compatable for automatic coupling, I cannot say if they are compatable for magnetic uncoupling but I suspect they would be.
Depending on the era you choose to model, railroads used a variety of coupler types until standards were mandated in the early 1900s. Some lines used what was known as "Link and Pin" couplers right up until standardization. (In practice, this type is a bit of a challenge for most people to use in regular operations)
The practice of interchange which developed during the ninetheenth century meant that most first class railroads adopted M.C.B. (Master Car Builders) standard type couplers long before safety standards were imposed. So while there was some variety in manufacture, the basic type of coupler was the knuckle type we know today. Eli Janney patented his knuckle coupler in 1873, so, if you are modelling a railroad anytime after 1873, you can feel justified in using the "modern" type coupler.
The McHenry coupler is the brand that Athearn uses on their cars and locomotives, other manufacturers use a coupler similar to these in most important characteristics. For the most part, these couplers are made to look like modern couplers and are very inexpensive. They couple and uncouple with ease and reliability when first installed. They are plastic, very oversized and seem to lose their reliability with time as the plastic parts, especially the centering springs, deform. The size alone makes them unsuitable for Early Era modellers.
Next is the Kadee coupler, in this case the "Scale Head" type. Kadee couplers come in a wide variety of types, many haveing specific prototype uses, but for the Early Rail modeller, the "Scale Head" is probably the most appropriate. These are metal with metal coil springs which acctuate the jaws of the coupler allowing them to couple automatically. I prefer the "Whisker" centering type over the old standard bronze spring type as I feel they are more reliable in the long run and easier to install. These couplers are smaller than the McHenery with nice realistic detail but perhaps a bit large for some Early Rail equipment.
Lastly, the Kadee Hon3 and 3/4 size coupler. The 3/4 size coupler (Kadee refers to these as "old time Coupler") #711 and the HOn3 coupler #714 are similar in all respects. These are plastic, two part, couplers with an internal coil centering spring. They require assembly (I assemble them with the magnetic trip lever in place and then clip it off with a flush cutter once installed) and are kind of a pain in the neck to get together. However, they are much smaller than either the McHenry or "Standard Head" and therefore quite suitable for the lighter, smaller Early Era equipment. I tend to use these on cars which would have been built before 1890.
Another advantage to using smaller couplers is in the area of "close coupling". This practice gives a much more realistic appearance to your rolling stock and is easier to achieve with smaller couplers...but, that is another story.