I can't remember the measurement details off the top of my head, but:
- S and small T axles have identical splines. Maybe 23 spline and 24mm diameter
- Large T and E axles have the same spline count (also same as S and small T) and measure at the same diameter, but are NOT interchangeable. Maybe 23 spline and 25mm diameter (25.3 in fact).
- F is bigger.
There was a famous photo that floated around back in the day showing the diameter of a small and a big T spline being measured. OK,
Hen