| Item | Common reference | Meaning |
|---|---|---|
| U.S. standard gauge | 4 ft 8½ in / 1,435 mm | Distance between inside faces of rails. |
| Freight-car wheels | Often 33 or 36 in | Common sizes vary with car type and capacity. |
| Road-diesel wheels | Often around 40–42 in | Varies by locomotive design. |
| HO scale | 1:87.1 | Popular model-railroad scale. |
| N scale | 1:160 | Smaller scale useful in limited space. |
Use equipment-specific engineering sources when an exact dimension is required.