What the numbers on the packet mean, and why the track you pick decides what your layout can do
Published 3 June 2026
Track is the one thing on a layout you cannot easily change your mind about later. Locomotives can be sold on, buildings can be moved, scenery can be scraped off and redone. Track gets glued down, ballasted, wired and buried under everything else. It is worth twenty minutes of thinking before you buy the first packet.
Set-track is sectional. Every piece is a fixed length or a fixed curve, the geometry is designed so that pieces click together into standard shapes, and you can build an oval on the carpet in five minutes. Hornby's own track and Peco's Setrack range are both of this type, and they are compatible with each other.
Flexible track, which Peco calls Streamline and most people just call flexi, comes in metre lengths of loose sleepers that bend to whatever radius you want. It costs less per metre, it produces far fewer joints, and it lets you use gentle curves that no sectional system offers. It also requires you to cut rail, file the ends, and hold the curve while you pin it down.
Most layouts end up using both. Set-track points and crossings in the yard where geometry matters, flexi on the running lines where a sweeping curve looks better than four fixed sections joined together.
British OO set-track curves come in four standard radii, which Hornby and Peco Setrack share.
| Curve | Radius | Diameter of a full circle |
|---|---|---|
| First radius | 371mm | about 780mm |
| Second radius | 438mm | about 915mm |
| Third radius | 505mm | about 1,050mm |
| Fourth radius | 571.5mm | about 1,185mm |
First radius is what comes in most train sets, because it is the only thing that fits on a small board. A little pannier tank and four short wheelbase wagons will trundle round it perfectly happily. A Duchess with a rake of Mk1 coaches will either refuse outright, or go round with the coaches hanging out over the sleepers at an angle no real railway ever managed.
The rule of thumb worth remembering: the longer the vehicle, the bigger the radius it needs. Bogie coaches, big Pacifics and six-axle diesels want third radius as an absolute minimum and look considerably better on fourth or on gentle flexi curves. If you are designing from scratch and the space allows it, build to third radius and you will never regret it.
The code number on a packet of track is the height of the rail in thousandths of an inch. Nothing more mysterious than that.
| Code | Rail height | Usual scale |
|---|---|---|
| Code 100 | 0.100in, 2.5mm | OO and HO, the traditional standard |
| Code 83 | 0.083in, 2.1mm | HO, closer to prototype |
| Code 75 | 0.075in, 1.9mm | OO finescale |
| Code 80 | 0.080in, 2.0mm | N, the traditional standard |
| Code 55 | 0.055in, 1.4mm | N finescale |
Code 100 rail in OO is considerably taller than scale. On a real railway, rail that size would belong on a heavily used main line, and even then it would look chunky. Code 75 is much closer to right, and the difference is genuinely visible once ballasted, particularly in photographs.
Points, or turnouts if you prefer, come in small, medium and large radius versions, plus curved, single and double slips, and Y points. Bigger radius points look better and derail less, and the same rule applies as with curves: use the largest the space allows.
The one decision that confuses newcomers is the frog, which is the V-shaped crossing where the two routes cross. Peco offers Insulfrog, where that V is plastic and therefore dead, and Electrofrog, where it is metal and live. Insulfrog is simpler to wire and perfectly fine for most layouts. Electrofrog gives more reliable pickup, which matters for short wheelbase locomotives that keep stalling, but the frog polarity has to be switched with the point blades. Peco's newer Unifrog design can be wired either way, which is a sensible hedge if you are not sure yet.
Points can be thrown by hand, by a surface-mounted point motor sitting next to the track, or by a solenoid or slow-motion motor under the baseboard. Under-board is tidier and considerably more work. Decide before you fix the baseboard down, because retrofitting a point motor under a finished layout means lying on your back with a drill.
Rail joiners hold track together mechanically. They also conduct electricity, right up until they do not. They loosen, they oxidise, and the layout that ran perfectly in March becomes intermittent by October.
The fix is to solder droppers: short lengths of wire from each rail down through a hole in the baseboard to a heavier bus wire running underneath. Every metre or two of track, and every isolated section. It is dull work and it is the difference between a layout that runs and a layout you keep prodding.
This applies to DCC even more than to analogue, because a digital command station is feeding both power and data down the rails. A weak connection produces intermittent decoder behaviour that is maddening to diagnose. A bus of reasonably thick wire with droppers every so often solves most of it before it starts.
Track pinned straight to a plywood baseboard is loud. The board acts as a soundbox and a passing train sounds like a filing cabinet falling downstairs. Cork underlay or foam roadbed under the track deadens most of that and gives you the raised ballast shoulder that real track sits on.
Ballast goes on afterwards: spread dry, groomed into shape with a soft brush, wetted with water containing a drop of washing-up liquid to break the surface tension, then dribbled with dilute PVA. Do a short section first and let it dry before committing to the whole layout, because everyone's first attempt is too thick.
Dirty rail is the single most common cause of stuttering locomotives. A track rubber removes oxidation quickly, but it is an abrasive and it leaves fine scratches that attract dirt faster next time, so use it sparingly. Isopropyl alcohol on a lint-free cloth or a proper track cleaning pad does a better job for routine cleaning and does not damage the railhead.
Never take a track rubber to locomotive wheels. Clean those with alcohol on a cotton bud while the loco sits on a rolling road or upside down in a cradle.
Track packs work out cheaper than loose pieces if the plan they are designed for is roughly what you want. If it is not, you end up with a drawer of unwanted short straights. Buy the points first, since they are the expensive bit and they dictate the geometry, then fill in between them with flexi.
And before any of it, mock the whole plan up on the actual baseboard with track laid loose. Run a train round it. Things that look fine on paper turn out to be unreachable, ugly or six inches too long surprisingly often, and loose track can still be picked up and rethought.