Kato Unitrack · HO scale
Kato HO Unitrack basics
Kato's HO Unitrack is a smaller, stricter range than the N line: every standard curve is 22.5°, the straights are fixed lengths, and there are no bridges or viaducts to elevate. Here is what is in the box, from the catalog RailMind models.
Curves: 22.5°, sixteen to a circle
The standard HO curves are all 22.5° arcs — 16 pieces make a circle — at radii stepping by 60 mm: R370 (2-280), R430 (2-260), R490 (2-270), R550 (2-210), R610 (2-220), R670 (2-230), R730 (2-240) and R790 (2-250). Beyond those are two odd arcs: the R867 fitting curve (2-290) at 10°, 36 to a circle, which exists to close the #6 turnout's geometry; and the broad R1546 (2-321) and R1606 (2-331) at 11.25°, 32 to a circle. An HO oval is therefore sixteen curves and two equal straights, which is why RailMind's free tier is 20 straights and curves in HO against 16 in N.
Straights: fixed lengths only
Ten lengths, all exact millimeters: S60 (2-105), S94 (2-111), S97 (2-192), S114 (2-120), S123 (2-140), S149 (2-193), S174 (2-130), S227 (2-160), S246 (2-150) and S369 (2-180). Kato also sells HO flex (2-000) and an expansion track (2-194); like their N counterparts, RailMind leaves variable-length pieces out so a plan cannot close on a length you cannot buy fixed. Most straights and curves come four to a pack; S94, S227, S149 and the R867 fitting curve come two to a pack, and the 109 mm bumper (2-170) is sold in pairs.
Turnouts and the one crossing
- R490 turnout (2-840 L / 2-841 R) — a 3 mm straight lead, then a 22.5° arc of R490, its own frog angle; it is not a #4.
- #4 (2-850 L / 2-851 R) — a 186 mm through route that diverges at R550 over 19°, not 22.5°. The box adds two S61 adapters, L and R (186 + 61 = the 246 mm often quoted), an S114 and two short R550 fillers: 3.5° on the diverging leg lands it on the 22.5° grid.
- #6 — two different pieces. The powered #6 (2-860 L / 2-861 R) has a 246 mm through route; the manual #6 (2-862 / 2-863) has 343 mm. Both diverge on R867 over 10° plus a straight tail, and the R867/10° reverse curve from the box brings the siding parallel on Kato's 60 mm HO track center (the powered #6 reaches it 492 mm along, with the box's S97).
- 90° crossing (2-401) — the only rail diamond Kato makes in HO; two 60 mm routes, the same 60 mm as the double-track center.
Service pieces round out the range: an S246 feeder (2-151), a 123 mm rerailer (2-142) and 123 mm uncoupler (2-143), and the bumper.
What HO does not have
Kato publishes no HO bridges, viaducts, double-track pieces, turntables, wye turnouts or curved turnouts. The elevated range — the viaduct straights and curves, and the piers (23-015/017) that carry them — is N-scale only. An HO plan in RailMind is a ground-level plan of straights, curves, turnouts and the crossing, and the app refuses to drop an N piece into it or the reverse; a plan is one scale.
Closing an HO loop
The rules are the N rules with different numbers: curves summing to 360° — sixteen 22.5° pieces at one radius — and straights that match side for side. Concentric HO ovals are 60 mm apart, one radius step: R490 inside R550, R550 inside R610, and so on up the 60 mm ladder. RailMind's gallery has seven HO plans, four of them Kato's own; three to start from are an R490 Starter Oval with two S246 straights per side, a Wide Mainline Oval on R610, and an Oval + Passing Siding that drops its siding through #6 turnouts and R867 curves onto the 60 mm center. The structure of the first is the same as the N Starter Oval below, with sixteen curves where N has eight.
See it in a plan
The N-scale twin of the HO Starter Oval: same rule, eight curves instead of sixteen. Starter Oval →
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