HO track codes explained: code 100, 83, 75 and more

Step by step

1. 1

   Step 1: Read the number

   Rail code is the rail height in thousandths of an inch: code 100 ≈ 2.5 mm, code 83 = 0.083 in ≈ 2.1 mm, code 75 ≈ 1.9 mm, code 70 ≈ 1.8 mm. Lower codes look finer and more like real rail.

   Next: step 2
2. 2

   Step 2: Know where code 100 fits

   Code 100 is the most common and the most forgiving: Peco's OO/HO code 100 Streamline allows flange depths up to 1.6 mm, so older models with deep flanges still run. It is over-scale — it represents very heavy rail.

   Next: step 3
3. 3

   Step 3: Know where code 83 fits

   Code 83 is popular with American-outline modellers. Peco's HO code 83 range is North American in style and, according to Peco's product description, follows A.R.E.A. drawings and NMRA standards. Atlas also sells HO code 83 and code 100 track. Trix C-track rail is 2.1 mm high — the same as code 83 — and Roco lists 2.1 mm rail on its RocoLine and geoLine track.

   Next: step 4
4. 4

   Step 4: Know where code 75 fits

   Peco's OO/HO code 75 Streamline (wooden, concrete, steel, bi-bloc and bullhead sleeper versions) is aimed at modern, finer-wheeled models. Most current models run on it, but some older models with deep flanges may not clear the rail fixings.

   Next: step 5
5. 5

   Step 5: Join different codes properly

   Don't just squeeze a rail joiner over two different rail heights. Use a transition track — Peco makes SL-113 (code 75 to code 100) and SL-116 (code 83 to code 100) — or carefully shim and solder.

   Next: step 6
6. 6

   Step 6: Remember: set track is its own system

   Märklin C-track, Roco geoLine, Piko A-track and Kato Unitrack each have their own geometry and joiners. Each maker sells adaptor pieces for its own systems, but joining one maker's set track to another's usually needs a suitable transition or adaptor.