So, replaced a chewed up Hope Pro2 freehub with a steel one. All good.

Put the 9 spd cassette on and fitting the end cap, tighten it up and its all still loose. Put a spacer behind the cassette and I cant fit the end cap as the threads dont engage.

I notice that the grooves on the freehub extend past a small section of metal so the cassette slides on a long way making me think I need a spacer but when I fit one, the cassette doest seem to go on far enough…

All the spacers between cogs are present and correct.

Any thoughts?

Washer between hub body and freehub

Would that make a difference Tom? The hub has the thread for the locking cap cut into one end so nothing on teh freehub where the cassette is mounted, can change size….

A thinner spacer?

1mm spacer is probably the answer

Isn’t the hub now road 11 speed compatible so needs a thin spacer (about 1mm) to work with anything else.

look at the freehub pictures at the bottom.

Thanks, that link is very useful. Pictures help.

Well, I have sorted it. Every day is a school day so this is what I found out.

The end caps for this Hope rear hub are “sided”, as in they are specific to each side. Crucially, the one on the freehub side has a different shape to allow engagement with teh spline tool to match cassette lock rings.

Wrong end cap, tool doesnt fit.

Combined with the very thin washer, all now good. Thanks for your help one and all.