Each scale standard is mandatory only at the joining face — the rails, the bolt-up edge, the polarity. Inside the module the modeller is free to lay out scenery, structures and operating ideas however they like. These pages collect the dimensions, tolerances and conventions that make any two modules — built ten years apart, in two different states — clip together and just run.
The four Australian T-TRAK scale standards differ in track gauge, module footprint and recommended track system, but a small set of universal rules holds them together. These rules are what make a single layout possible: an N module joined to an N module from interstate, or four HO modules from four different builders forming a clean corner. Memorise these — they apply to every scale, every module, every meet.
The first and most important is the joining-face rule. The track ends sit precisely 1 mm inside the module front and back edges. That overhang means the module body never fouls the rails of the neighbouring module, and small variations in plywood thickness or skin glue-up are absorbed at the gap rather than at the rails. The module length therefore equals the chosen track length minus 2 mm — never minus zero, never plus a fudge factor.
The second universal rule is polarity. Every Australian T-TRAK standard wires the BLUE bus wire to the outer rails (the two rails on the front and back faces of the module pair). The WHITE bus wire goes to the inner rails. Get this right at every feeder and a hundred modules will run as one continuous railway. Get it wrong on one module and the booster will trip every time that module is plugged in.
| Rail-end overhang | 1 mm inside front & back edges | Same on every face that joins to another module. |
|---|---|---|
| Module length | track length − 2 mm | Two times the 1 mm overhang. |
| Polarity convention | BLUE → outer rails | WHITE → inner rails. Mandatory at every feeder. |
| Mainline gradient | 0 % | Mains are level; only branches/spurs may climb inside the module. |
| Module box height | 70 mm | Top of railhead to underside of base, before levelling feet. |
| Levelling adjustment | up to 100 mm | Bolts or feet under the box, used to bring the module into plane. |
| Front face is south | scenic / public side | Skyboard rises from the rear edge; controls on the operator side. |
| Joining method | M6 bolt + locating pin | Or scale-specific equivalent — see the per-scale page. |
Numbers in this guide are presented in monospace so a builder reading on a phone in poor lighting at a club night can still tell 308 from 300. If a measurement matters, it is in mono.
The table below collects the headline numbers for all four scales in one place. Use it for quick checks; for the full picture, every row links through to the scale-specific page where the dimension is illustrated in context.
| Parameter | N | HO / OO | TT | Mini-T |
|---|---|---|---|---|
| Scale ratio | 1:160 | 1:87 – 1:76 | 1:120 | 1:160 |
| Track gauge | 9 mm | 16.5 mm | 12 mm | 9 mm |
| Track system | Kato Unitrack | Kato HO Unitrack | Tillig Bedding | Kato Unitrack |
| Single straight L × D × H | 308 × 300 × 70 mm | 490 × 490 × 70 mm | 413 × 400 × 70 mm | — × 150 × 70 mm |
| Track centres | 33 mm | 60 mm | 43 mm | 33 mm |
| Front rail setback | 38 mm | 75 mm | 86 mm to centre | — |
| Multi-length step | 310 mm | 492 mm | 415 mm | 62 mm |
| Outside corner footprint | 365² mm | 705² mm | 481² mm | 290² mm |
| Inner mainline radius | 282 mm | 550 mm | 353 mm | — |
| Outer mainline radius | 315 mm | 610 mm | 396 mm | — |
| Vertical clearance | 45 mm | 80 mm | — | — |
| Side clearance, straight | 12 mm | — | — | — |
| Side clearance, curve | 15 mm | 30 mm in / 20 mm out | — | — |
| Skyboard visible height | 200 mm | 350 mm | optional | optional |
| Feeder hole positions | 45 / 78 mm | 96 / 156 mm | — | 45 / 78 mm |
| Feed cadence (DC) | ≥ 1 per 9 m | ≥ 1 per 9 m | ≥ 1 per 9 m | ≥ 1 per 9 m |
| Feeder track part | Kato #20-041 | Kato #2-151 | Tillig feeder | Kato #20-041 |
| Polarity rule | BLUE → outer | BLUE → outer | BLUE → outer | BLUE → outer |
A dash — in a cell means the value is either not formally specified for that scale (Mini-T's vertical clearance, for example, is left to the modeller because there is no overhead requirement at 1:160 in such a small footprint) or is documented elsewhere in a way that doesn't reduce to a single number. Always check the per-scale page before cutting timber.
The "multi-length step" is the increment by which a longer-than-single module grows: an N double is 2 × 310 − 2 = 618 mm long, a triple is 3 × 310 − 2 = 928 mm, and so on. The same arithmetic applies in every scale; only the step changes.
Four scales, four pages. Each one expands the headline numbers in the comparison table into the full specification — corner geometry, clearance envelopes, recommended track parts list, electrical layout, skyboard rules and the small print that distinguishes a clean module from a wobbly one.
The most common Australian T-TRAK scale and the best supported. 308 × 300 mm single straights on Kato Unitrack, two-track mainline at 33 mm centres, full corner geometry and skyboard convention. If you're starting from scratch, start here.
Read N-scale specificationsFor modellers in 1:87 (HO) or 1:76 (OO British outline). Single straights are 490 × 490 mm on Kato HO Unitrack, mainline centres widen to 60 mm and the curve setback grows accordingly. A heavier, more visually substantial layout.
Read HO/OO specificationsAdded in v2.0.3, TT sits between N and HO at 1:120. Single straights are 413 × 400 mm on Tillig Bedding, with mainline centres at 43 mm. Less common than N or HO but well-supported by European model manufacturers.
Read TT-scale specificationsA reduced-depth N-gauge variant for modellers tight on transport space or club table. Same 9 mm gauge and 33 mm centres as N, but only 150 mm deep, with shorter length increments to suit a single shelf or backpack.
Read Mini-T specificationsIf you've come to T-TRAK Australia from the original North American or Japanese T-TRAK pages you'll notice some numbers don't match. That isn't error — it's a deliberate localisation. The Australian standard has been adjusted in four areas to suit our timber sizes, our mains supply, and our climate.
Module depth. The Australian N standard is 300 mm deep, where the international convention is 210 mm. The deeper module gives more usable scenery area and accommodates a more substantial skyboard at exhibition height; the joining face is unaffected, so an Australian module still couples to an international one if you can live with the visual mismatch behind the trains.
Available timber. Hobby timber here is metric. We assume 6 mm MDF for the N-scale top and 12 mm hardwood ply for the Mini-T base, both readily stocked at Bunnings and most timber yards. Imperial-thickness ply (¼″, ½″) is harder to source and is not assumed in the construction notes — if you have it, treat it as equivalent.
Mains supply. Wiring conventions are written for 240 V AC mains practice, with all bench transformers and DCC boosters specified for Australian three-pin supply. The polarity convention for the track bus is independent of mains voltage, but the recommended power-supply parts list assumes Australian-market product.
Safety. A 30 mA RCD is mandatory on the meet's mains feed — see the Electrical and Meets pages. This is non-negotiable at any public exhibition under Australian electrical safety expectations, and most venues will require sighting of test-and-tag tags before allowing setup.
Paint chips. The recommended skyboard sky-blue and ground-tan are matched to commonly stocked Australian paint-shop chips (Dulux, British Paints), so a builder can walk into a paint shop and ask for the chip by name rather than mail-ordering a US hobby colour. Per-scale pages list the chip codes.
Two further notes worth flagging here rather than burying in the per-scale page. First, the Australian standard explicitly does not specify a humidity tolerance for the timber — a Townsville module and a Hobart module will both build true if you respect the joining-face dimensions, and any seasonal flex is absorbed by the levelling feet. Second, the timber thickness affects only the box; the 70 mm module-box height is measured to the top of the railhead, so different ply choices don't change the running height of the layout.
If your local club has agreed to deviate from any of the Australian deltas — for example, by running an all-international-spec layout for a one-off event — note the deviation in the meet brief so visiting modellers know which face geometry to bring. The standard accommodates exceptions; it just doesn't hide them.