I need to fix a single speed freewheel onto a 25mm shaft. Any ideas of a part to start with and modify? Seen the surley Fixxer and something called Drew’s adapter but neither is ideal.

I think if you look on trike racing and velocoar websites you may get a few ideas.

Otherwise cut up an old freewheel fixed hub and open it out to fit the shaft, then weld on. (I’m chucking one out if you want one)