UPDATED
Official size and measured Lug to Lug :
- F5s : 42mm x 14.5mm / Lug to Lug : 52mm
- F5 : 47mm x 15.5mm / Lug to Lug : 56mm
- F5x : 51mm x 17.5mm / Lug to Lug : 58 mm
- FR235/630 : 45mm x 11.7mm / Lug to Lug : 50mm
- FR735xt : 44,5mm x 11.9mm / Lug to Lug : 48mm
- FR935 : 47mm x 13.9mm / Lug to Lug : 53mm
This might not tell the whole story though as the lugs seem to stick out quite a lot on the F5s and that contributes to how the watch will "sit" on the wrist.
I've measured the lug to lug length at 56mm on the F5 (50mm on the FR235), can anyone with a 5s or a 5x do the same ?