There's a couple of differences between the 372s and 393s. Whilst the wheelbases are shared at 7'3" x 8'3", plus the wider overall width compared to the Southern Railway Ns and Us, there's also:
- 372s: 5ft 6in drivers; 393s: 6ft drivers
393s had a deeper drop in the footplate in order to maintain the same buffer centre heights as the 372s, plus small splashers over the topsof the drivers.