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Kato Unitrack · N scale · 33 mm centers

Kato Unitrack double-track spacing: 33 mm

Kato N-scale Unitrack puts parallel tracks 33 mm apart, center to center. The curves are cut so that this spacing comes out of the catalog rather than out of your hands.

33 mm, everywhere

The double crossover (20-210) is 310 mm long with its two mains on exactly 33 mm centers. Kato's double-track pieces put both mains on one roadbed at the same spacing — RailMind's Concrete-Tie Oval example is built from them — and the T-TRAK standard runs its two mains on the 33 mm center as well. Anything you build to sit beside a main sits at 33.

Concentric curves

Two ovals stay a constant distance apart when their straights are equal, their curves have the same arc, and their radii differ by the spacing — then the curve centers coincide. Kato's radii step by 33 mm through the range, so almost every curve has a concentric partner one step in or out:

R348 is the hinge: it comes in 45° (20-132) to pair inside with R315, and in 30° (20-130) to pair outside with R381, which is 30° only. R481 (15°, the #4 turnout's diverging radius, also sold as the 20-472 curved deck bridge) pairs only with the R448 curved girder bridge; R718 (15°, the #6's radius) has no partner 33 mm away in the catalog. The viaduct curves repeat the ground radii — R249, R282, R315, R348 at 45°, R348 and R381 at 30° — so the same pairs work elevated.

RailMind's Double Oval + Crossover is the R315/R348 pair: 348 − 33 = 315, both loops on 806 mm straights, joined by the crossover. Its parallel-copy tool does the same swap for you — copy a run 33 mm across and every curve changes radius to stay concentric.

Getting there with a turnout

A siding is parallel track too, and a turnout has to drop it the 33 mm. A #4 (20-220/221) diverges at R481 over 15°; follow it with an opposite-hand R481-15 (20-160) and the diverging track is parallel again at 32.779 mm — the 0.22 mm short of 33 is real and is taken up by rail-joiner slop. A #6 (20-202/203) diverges at R718 over 15°, and with its R718-15 (20-150) reverse curve lands at 48.931 mm, close to the ~49.5 mm a real #6 center measures. RailMind counts anything within 2 mm as joined, so both close on screen exactly as they do on the table. The Oval + Passing Siding is the #4 case with a 498 mm run — S248 + S186 + S64 — between the two reverse curves.

HO is 60 mm

Kato's HO Unitrack track center is 60 mm, not 33. The HO 90° crossing's two routes are 60 mm for that reason, and an HO #6 with one R867/10° fitting curve lands its siding on the 60 mm grid. More under HO Unitrack basics.

See it in a plan

R348 outside R315, both on 806 mm straights, joined by the double crossover. Double Oval + Crossover →

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