If you are, brought up on British steam locomotive designs, so to speak, it comes as something of a culture shock when you first see those of other European countries. One of the reasons is that Britain has the smallest loading gauge, and this may have had far-reaching effects on locomotive design.

For example, feed-water heaters have never been popular in Britain, though used extensively by almost all other countries. It has been suggested that this is because working within the British loading gauge it was very difficult to find anywhere to put them.
Likewise a Franco-Crosti boiler with side pre-heaters (as much used in Italy) was impractical, so Britain's only Franco-Crosti, the 9F, had a single preheater under the boiler.

There is clearly a major effect on maximum cylinder size; many USA designs have cylinders that look enormous to British eyes.

The Russian loading gauge is the largest, and that is why Russian locomotives look so big. They are so big.

---