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Module Standards

By Jim Pasquill – Updated October 24, 2002.


Height to the top of the rail is 48″.

Most of the modules built so far have 45″-long legs with a 1″ standard extension on an adjusting bolt or leg leveler (so it can go up or down about 7/8″). This is a 46″ leg, which leaves 2″ for the module top, track support, and track. Placing the rail height 2″ above the leg height leaves room for scenic features below the track, and other flexibility such as a spur with a downgrade.


The center of the mainline track is 6-7/8″ from the BACK edge of the module measured from the face of the backdrop. If you want to build a module with your track running through the backdrop to a staging area you may, as long as the visible portion of the mainline crosses the ends at 6 7/8″ from the face of the backdrop.

Why the odd setback? When Chris McChesney, Jim Pasquill, and then Dave Frary built modules to connect this was the setback that worked for them. Bob Hayden soon followed and then others. Thus a precedent was set which may be odd, but it works fine and is no stranger than HOn30 itself.

Having the mainline toward the back allows placing the interesting stuff — spurs, industries, depots, turntables, and so forth in front of the main line and toward the viewer and reinforces the impression that the trains are running through the scenery instead of in front of it.

The mainline must cross the module boundary at a 90-degree angle except as noted below.

Module pairs that will always be mated may have a non-standard setback at their internal boundary and may cross their internal boundaries at a different angle.

If enough members of an operating group want to establish a standard for a main in another location they may do so, preferably in consultation with the other groups so that a universal “alternate” standard may be adopted.


The top of the rail must be 48″ above the floor, and the joining section must be code 70 except as noted below.

Minimum mainline rail size is code 55, with code 70 recommended

The mainline must end 3″ from the end of each module requiring a 6″ code 70 joiner section. Currently most of us are using Micro-Engineering code 70 flex-track for the joiner and the main. Some are using Shinohara code 70 N scale flex track as it is more flexible than ME track. However, note that Shinohara track has higher ties than ME so you must compensate for that or it may cause problems in getting the joiner to lay flat. Any other kind of track can cause similar problems so be prepared to adjust either the height of the track or depth of the area that the track occupies.

Owners of modules that choose to use rail of a code other than code 70 must bring their track to code 70 before the joiner track.

Owners of module pairs that have the same track code other than code 70 may use a joiner track of the same code. For example, there is no need to have a code 70 joiner between two code 55 modules if the owners supply a code 55 joiner. Code 70 was chosen as a good compromise between those who use code 55 rail and those who use code 80/83 and with readily available code 70 track and turnouts it is the preferred choice.

We use the NMRA N-gauge standards gauge for track and turnouts.


Parallel to the main tracks must be at least 1 ½” apart on centers, with 1 3/4″ or more preferred.

If you plan to join parallel passing sidings with other’s modules the passing siding must be 1 ¾” on centers from the main and end 3″ from the module end. The current preference is to have passing sidings that extend from one module to another in front of the main. Check with your local operating group.

All parts of road crossings should be 1/64″ lower than the rail top. Flangeways through crossings, like turnout frogs, must be to NMRA N standards.

Building and platform clearances should be a full HO scale 36″ from the outer edge of the outer rail.

The NMRA HOn3 standards gauge is a good tool to use to assure proper track clearances in HOn30. If you have a friend in HOn3 borrow his gauge and trace it onto some hardboard, cut it out, then mount it on a stick creating a useful gauge that can be run though a module with less chance of knocking something with your arm.


The minimum is an 18″ radius for the mainline and passing sidings. For any other track the radius is up to the owner but keep in mind that the tighter the radius the fewer cars and locomotives that will be able to run on parts of a module.

Turnouts: Minimum No. 6 off the main to spurs and sidings that are built to the mainline standards. The mainline should go through the straight leg of switches.

Grades: The current members prefer that the main and designated passing sidings have no grade at all. The net grade allowed is “0”. Before designing a module with a grade on the main and passing sidings please discuss it with the members you plan to be operating with.


We use the NMRA N gauge standards gauge for wheels, Microtrains couplers and the Microtrains MT-1055 gauge for coupler height. Rolling stock to be used in a mix with other owner’s rolling stock must have body mounted couplers.


Backdrops should extend at least 12″ above the top of the rail. 14″ is better and we are encouraging folks to accept 14″ as the standard. Each local group has chosen a standard sky color. Please contact the members for the latest.


You may use ANY materials they wish as long as the modules can be mated. It is critical that the end of each module be perfectly flat and squared, without any protruding points or uneven areas that can result in modules not mating flush. Modules must be the exact stated length, i.e. a f our foot module should be four feet and not four feet and a quarter inch, as minor variations can make it impossible to complete an oval or other continuous layout.

There are no required scenery contours. However, we welcome it if you want to try to work closely with one or more of your members so that your modules match.

Check with your local group for standard facing colors and other requirements such as skirting.


The standard is a single-track mainline. An individual can have any number of tracks crossing the internal boundaries of modules that are always to be mated to each other.

Module width: minimum 20″; maximum 30″, 24″ is recommended. Local groups can allow deviations according to their own desires. For the sake of esthetics, it is recommended that modules wider and thinner than 24″ have front ends contoured to bring the module in or out to 24″.

Length is not proscribed, but 4′ is what most are using. While a 4′-long scene in HO scale doesn’t allow for much scenery and track, pairs of 4′ modules can make excellent scenes. 3′ modules are allowed if that is all you have space for. Paired 3′ modules offer more flexibility and are particularly easy to transport if stacked. For ease in setup at larger shows it is preferable to have module sets in multiples of 4′. If you want to build modules that are not in multiples of 4′ please check with your intended operating group. You may be asked to provide a unit that will bring your total module length up to a multiple of 4′ so that a loop can be completed.

Our modules are operated from in front (facing the module) so turnout and electrical controls should be in front.

Corner standards: Local groups can decide if they want to create layouts that have inside or outside corners, or use loops at the end of point to point layouts. Several corner designs are in use by the groups in New England and the West Coast. Contact them for details.


We use a standard 3″ C-clamp, per NTrak. Top of rail to inside edge of the spine of C-clamp not to exceed 4-1/2″. Some members are using large spring clamps that are also acceptable.


Here is a method used by Bob Hayden that you can use to bring code 80 Peco track down to the standard code 70 joiner. You can use a similar procedure to bring code 55 up to the standard code 70 joiner.

To bring the Peco code 80 track on the module down to code 70 for the transition, cut the rail out of the Peco code 80 flex-track for the last 2″, but leave the ties. Slip a rail joiner halfway onto the end of the code 80 rail, then flatten with pliers so it’s roughly .010″ thick. Solder code 70 rail on top of joiner and to end of code 80 rail, then file smooth. Paint it, and you’ll have a hard time even seeing it after you add ballast. If you want to be fussy, slip a strip of .010″ Evergreen styrene under the Code 70 rail to shim it up against the molded flex-track spikes. If you don’t want to use stock N gauge code 70 flex, module to module joiner sections can be made by replacing the code 80 rail in Peco flex-track with code 70 rail.


See the separate document on wiring. Currently most members have their modules wired as one cab with ability to cut power to sidings. This is acceptable for now but the two cab system in the proposed wiring standard is what the groups involved have agreed to work toward. You need not build in many blocks. Your whole module can be one block if any sidings can be powered off.

The West Coast group is using DCC so check with them for any different requirements.

A basic module drawing, showing the minimal dimensions, by Bert Greeley.

Check out what the New England and Midwest HOn30 Guilds and the West Coast groups are up to at:

Jim Pasquill
Jim at

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