Trying to put a 10speed xt cassette on 8speed Hope hub.
I bought a 1.75mm mavic Spacer just to do this.
However there isn’t room to fit the lockring with spacer fitted, it looks perfect without.
So is the spacer necessary?

I think the theory is SRAM cassette no, Shimano yes but I never bothered. Did think its was that thick though. 1mm?

it is an official mavic m10 r.hub spacer

You don’t require a spacer at all for that combination.

I thought 7-8-9-10-shimano mtb 11speed cassettes all used the same freehub?

Afaik only 10sp Shimano roadie cassettes need a spacer. Not sure about SRAM road stuff as I’ve never fitted one.

I thought 7-8-9-10-shimano mtb 11speed cassettes all used the same freehub?

Nope. 7sp is narrower and only takes 7sp.
8,9,10,11sp MTB is all the same. 11sp road is wider and needs a specific freehub body. 🙂

EDIT
Just re read your post and yes you’re right about Shimano MTB stuff, and I just agreed with you. 🙂
7sp will fit an 8/9/10sp body but not the other way round.
Phew. All clear now. 😉

EDIT 2
There are some road freehub bodies about (Shimano only afaik) that will ONLY take a 10sp Ultegra or above road cassette. They were built with deeper splines in the same pattern for alloy freehub bodies.

thanks
I was worried, I dont recall where/what I read about needing the spacer

You will need a spacer for a 7speedcassette on a 8/9speedhub