October 28, 2026
How to Read Kato Unitrack Part Numbers and Track Diagrams
Hobby articles / Model Railroads
By LootBandit
Browse the Model Railroad Control, Track, and Troubleshooting Guides collection.
A Kato UNITRACK part number is a product identifier, not a universal formula for the piece’s dimensions. To read a track plan correctly, look up each number in Kato’s current parts list, then use the stated length, curve radius and included angle. On many N-scale track drawings, a notation such as R249-45 means a curved section of 249 mm radius that turns through 45 degrees. The catalog number, such as 20-100, identifies the item to purchase.
Start with the bill of materials
A manufacturer’s plan normally separates a diagram showing the layout from a list that gives a quantity, stock number, and description. The drawing may label a curve by radius and angle while the bill of materials gives its sales code. Follow both. A label that says 248 mm is a length, not necessarily a part number.
The Kato Corner Central plan is a useful example because it includes straights, curves, feeders, and left/right turnouts in one list.
| Example N-scale number | Kato’s listed piece | How to recognize it |
|---|---|---|
| 20-000 | 248 mm straight | Long common straight section |
| 20-020 | 124 mm straight | Half-length straight |
| 20-041 | 62 mm feeder track | Power connection integrated with short straight |
| 20-100 | R249-45 curve | 249 mm radius, 45-degree turn |
| 20-202 / 20-203 | No. 6 left / right turnout | Branching direction differs |
These are documented examples, not a promise that every number beginning with 20 follows the same pattern. Check each variant, package count, and scale when ordering.
Read radius and angle separately
The radius describes the distance from the center of the circle to the track centerline. The angle describes how far the section turns. On a continuous circle, eight 45-degree curves complete 360 degrees, assuming all eight share the same radius and there are no additional pieces. Twelve 30-degree curves would also close a circle of their own radius.
That calculation does not prove every locomotive can run the circle. A long rigid wheelbase can require a much wider radius than a tiny switcher. Check the rolling stock maker’s minimum recommended radius before buying compact curved pieces.
Watch the difference between N and HO catalogs
Kato sells UNITRACK in more than one scale. A similar-looking code from another scale is not interchangeable with the N-scale 20-series examples here. The manufacturer’s HO catalog uses other stock numbers; always specify scale and actual item number in your shopping list. A diagram copied from the internet without a scale label is incomplete purchasing information.
Turnouts are not just short curves
A Kato turnout’s description tells you its handedness and numbered geometry. Left and right are typically determined from the point end looking toward the diverging route. But a turnout is more than one curved section: the length along the straight route, where the branch diverges, and any included matching sections all affect the plan.
For instance, Kato lists a No. 4 turnout with companion short straight sections on certain plan lists. If you replace a No. 6 with a No. 4 because it “looks close,” the track may not meet at the far end of the siding. Use the correct part and its footprint from the chosen scale’s diagram.
Count feeders and small pieces
A single catalog line can represent a small component that matters electrically or geometrically: an insulated UniJoiner, a terminal joiner, a feeder section, an expansion section, or a 29 mm filler. Leaving one small straight out may put a curve into an unwanted kink at the next turnout. Forgetting a power feed can leave an isolated siding unable to run.
Kato’s Scenic Ridge bill of materials illustrates these details. Read its advice to lay out and mark the actual pieces before construction; rushing directly into foam grades or scenery is a common way to discover a diagram no longer fits.
Turn a diagram into a reliable buying list
- Confirm scale, diagram revision, and intended footprint.
- Copy each stock number with its quantity and full description.
- Separate single components from multi-piece packs before ordering.
- Verify the turnout direction, radius and angle, and special feeder or insulation parts.
- Build the plan loosely on the tabletop and mark the centerlines only after it fits.
- Roll a locomotive and your longest car through the intended routes before committing to grades or ballast.
Treat the catalog number as an exact lookup key, the geometry label as the explanation of how it fits, and the physical layout as the final test. That approach prevents expensive errors and makes future expansion much less frustrating.
