I believe the length needs to be calculated in?
It would matter to me if you are trying to design a 1 piece application or production type relibilty factor you want. If weight or cost is an issue? If those are not factors then you can oversize. if weight is an issue then a hollow drive shaft...
If you don't have access to a load cell etc... Easiest in my mind would be a cylinder with known area. Build a simple jig or using some slings to keep cylinder alligned. With either a simple hand pump or powered moving a simple cylinder against leg til it slips. You can record the pressures...
