Maine Sn2 Coupler FAQ:

The Sn2 Coupler FAQ provides inquiring minds the details behind the Sn2 coupler standard.  The information below wass captured by Jeff Saxton from various email discussion on the Sn2_Trains email list at yahoogroups.

The Sn2 Coupler FAQ; compiled by Dave Keith

The following standard has been developed through extensive list discussions occurring over a several month period of time.

The members of this list have adopted a standard for Maine 2-foot modeling.

  • Coupler: Kadee HOn3 #714 or HO “Old Time” #711 couplers, with the trip pins snipped off.
  • Body Mount Height: 18″ in S scale = 9/32″ actual.
  • Coupler Centerline Height: 14.5″ in S scale = .226″ actual.

This is derived from mounting the #714 couplers at the required BODY height.

Why the HOn3 (#714) or HO Old Time (#711) coupler? The knuckles of the #714 and #711 couplers are the closest to the size of an S scale Maine 2-foot coupler. HO and N scale couplers are either too big or too small (more information pertaining to the HO and N couplers below)

For all remaining answers in the FAQ, I will use HOn3 or #714 when referring to the couplers. The #714 and #711 are the same size, the only difference is the trip pins.

How did you get 18″ for the body height? Most of the freight cars on the Maine 2-foot railroads have an 18″ body (sill) height from the railhead. There were some exceptions, but 18″ seemed to be the most common height.

Most Maine 2-footers had a coupler height of 16″ (to coupler centerline), so isn’t 14.5″ too low? Yes, 14.5″ is too low. However, a compromise had to be made because the mounting box of the HOn3 coupler is thicker than that of a real 2-foot coupler. The HOn3 coupler is 3.5″ from box top to center of coupler, but the prototype couplers were only 2″.

Therefore, one of 3 compromises had to be made:

  1. Raise the body height
  2. Recess the couplers into the body
  3. Have lower couplers

For esthetics and simplicity to build, we chose to compromise coupler height. This way the car will ride at a prototypical height and have the couplers mounted on the bottom of the body like the prototype.

Why are the trip pins clipped off? Because we mount the Kadee couplers lower than the NMRA standard for HOn3, and as such, the trip pins would hit the rails when going through a turnout. We plan to uncouple cars manually not magnetically.

Why wasn’t the HOn3 standard used for coupler heights? The HOn3 coupler height equals 18″ (to centerline) in S scale. Thus, it is too high for Maine 2-foot equipment. If we adopted the HOn3 coupler height, then the car bodies would have to ride high, or the couplers would have to be recessed into the endbeam of the car. The HOn3 coupler height gauge may be correct for prototypes other than the Maine 2-footers. The HOn30 folks chose the N scale coupler height, even though the N scale height is not right for HOn30 models of Maine 2-foot equipment. Thus HOn30 models have compromises that we did not want to have in Sn2.

What about Passenger cars? Most 2-foot passenger cars had body heights greater than 18″. More like 20″ or 22″. Thus they had a special mounting for couplers under the end platform. Sn2 models of Maine 2-foot equipment will have to have a similar mounting.

What about Locomotives? There are issues here that we have not yet addressed, as we do not yet have brass locomotives. We feel these will become easy to address once we have commercial locomotives; but for now, anyone building locomotives and mounting couplers should follow the above standards.

How do I get a coupler height gauge? Click to make a coupler height gauge or buy a coupler height gauge

What about 2-footers outside of Maine? Gilpin? Wales? The Industrials? The standard presented here is for Maine 2-foot equipment. It does not apply to other railroads. The Gilpin (in Colorado) used link & pin couplers mounted on the ends of the cars. I think many industrial railroads would have done likewise. One member of this group has chosen the HOn3 standard of 18″ for his Gilpin models. This is probably a reasonable compromise considering the Gilpin did not use knuckle couplers. The Gilpin cars had body heights from 20″ to 27″. If the HOn3 couplers are mounted on the bottoms of the cars at the 18″ height, then that means the bodies are 21.5″, and that is in the range of the prototypes.

What if I model a free-lanced railroad outside of Maine? Some of the members of this list are placing their 2-foot railroads outside the state of Maine. However, most are still inspired by the Maine 2-footers so they are opting for this standard as well.

Why an Sn2 standard at all? How many Sn2 modelers are there? Currently, the Sn2 segment of the market is small. But this group hopes that Sn2 will grow enough to support Sn2 products such as cars, locomotives and structures. We already have true Maine 2-foot trucks. Thus, we need a standard for manufacturers. Additionally, we may want to run models together or have a module meet. At such times a coupler standard will ensure that trains will stay coupled.


Addendum to Coupler FAQ. After several more exchanges on the various other makes and brands of couplers that may be possible to use in Sn2, we have updated the FAQ. Compiled by Jeff Saxton.

Kadee (Micro-Trains) N Scale Couplers:

Here are some thoughts on use of n-scale couplers

  • Pro: Come pre-assembled
  • Pro: Smaller, no interference for Sn2 equipment
  • Pro: Can be used with magnets at Maine 2-Foot prototype height (#714 cannot do this)
  • Pro: Compatible with 714 (they couple reliably)
  • Con: Actually too small for Sn2
  • Con: Does not couple on curves as well as #714
  • Con: Requires tighter (more exacting) standards for coupler height, not as much forgiveness as #714

Because the N-scale couplers mate reliably with #714 couplers, they are a viable substitute for tight situations where a #714 might not fit.  A #714 can be trimmed at the rear, but should that not be enough, an N-scale coupler may be the best choice.  Examples usage might be a short wheelbase car or a locomotive pilot.  If an N-scale coupler is used on Sn2 rolling stock, it should be mounted according to the coupler center height requirement.

Accumate HO “Scale” #1020 Couplers:

These “Scale” HO couplers are a good match in size for S-scale 3/4 couplers used on many narrow gauge railroads, but the #1020 coupler box needs to be modified. The #1020 uses a box which is narrower and should fit inside an HO standard gauge coupler box. They should adequately fit the narrower width confines of Sn2 with some shaving if one is concerned.

The 1020 couplers include a paper which essentially says (paraphrased): “when cut back in length to the internal bulkhead, they match the size of boxes from other commercial HOn3 coupler makers”. This almost has to refer to Kadee #714 couplers.

Pro: Closer to actual S Scale size. Con: Online purchasing is the only real option for these. Con: Mounting boxes need to be re-worked before use.

Sergent HO “Scale” Couplers:

The HO Sergent is designed to fit into a standard “#5” box as supplied with most HO kits. It is possible to mount them without any box at all by simply using a screw.

There are two primary problems with either the Sergents, Accumate or other brands mentioned. The first is that they are harder to find, and from smaller firms that may not even be around in ten or fifteen years (we think Kadee will be with us for some time yet). We have serious doubts that Sergents or Accumate will still be a viable production item in twenty years.

The second problem, especially in terms of these “off-brand” couplers, is the added work required to assemble them, and get them mounted, and then operating properly. Kadees, while not optimal, certainly are much more of a ‘brainless’ assembly and installation process, with less problems in designing new mounts for each new product as it comes along. There is also the added track record of a firm long in business, with replacement and repair parts as close as your nearest hobby dealer.

Kadee #58 or #78 “Scale” Couplers:

The #58 coupler box is far too wide to fit between the wheelsets of an Sn2 freight car. The #78 has a much narrower box. This subject was discussed on the HOn3 list previously, and while more than one person came forward and said that the #78 “worked” for HOn3 cars because the coupler box was small enough (they had tried it), Jeff Bissonette later noted that the #78 box is still too big. It won’t allow sufficient truck swing on cars where the distance from the end sill to the centerline of the bolster is 3′ 9″ or less, and it will foul the outer axle.

Another downside of the #78, is that they only come assembled (more expensive) and not all hobby shops carry them on a regular basis.

The problem with any Kadee HO couplers will still boil down to the coupler box itself, since that box is still the same basic item as used in the #5 Kadee coupler. The size of the box limits rotation of trucks on freight cars.

Link and Pin Couplers:

Grandt Line makes an On2 Gilpin Tram link and pin coupler set in plastic that is acceptable. Not perfect, but usable.

Alexander HO Sclae Link & Pin. They are too large for HO but will work for S Scale. They require a coupler box the same size as a Kadee #4 and use that style mounting. They might be able to be screwed to a car with no box at all. Does anyone have current contact information for Alexander Scale Models?

The Back Shop is now offering an On3 Link & Pin that drops into a standard KD #5 box.

Russ Simpson makes a West Side Link & Pin in On3 that is small and Mac Neil (available from Coronado Scale Models) makes a brass Gilpin On2 unit that is also very small.

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3 Responses to Maine Sn2 Coupler FAQ:

  1. Trevor says:

    Interesting thinking. Has it changed at all now that several more years have passed and new developments have occurred – eg: the introduction of Sn2 brass for Maine prototypes?

    • narrowtracks says:


      A thought provoking question….I’m not sure what you refer to as new developments. The only development I can think of is that Sergents are available assembled. While sergents are a great appeal to smaller layouts, I’m not sure they are for everyone, so not sure they should be a standard or RP.

      For me, the HOn3 coupler is easy enough to operate and is reliable. The extra depth the HOn3 coupler has over the n-scale coupler has helped in reliability on the Sn2 Crew setups. They modular setups have minor humps at the module joins, so a taller/deeper coupler is less likely to result in train separation.

      For me, I like having the true low slung body heights, like the prototype. So I continue to feel that a lower coupler is acceptable. The lower coupler has proven a challenge to fit to locomotives. The first batch of T&T forneys require custom modification to couplers on the front and modification to the brakes on rear truck. I asked Matt at T&T to make the second set of forneys (smaller versions) compatible with the standard. He said he would, but I’ve not yet confirmed that (Life is often more fun than playing with couplers). I know that one Sn2 Trains yahoogroup member has started using an n-scale coupler box with the HOn3 couplers. The smaller box has less interference with truck swing.

      Maybe other Sn2 modelers will chime in on their recent experiences.

      • Trevor says:

        Hi David: Well, new developments like rapid prototyping – which might allow one to make new coupler boxes with a narrower profile. And with the actually brass locomotives available, did that change the standard at all – or were they manufactured to the Sn2 coupler standard? Just curious. I remember from my On2 days that every model seemed to have its own, unique, coupler height or swing issues. Since very few people actually interchanged their equipment with other layouts, it wasn’t really an issue. I picked a coupler / box / height that worked for me and that was that. Cheers! – Trevor

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