Sorry, I was making a couple of assumptions -
It's a 11-34 cassette.
It came with the 1.85mm spacer
Trying it on the 10 speed free hub with the spacer didn't fit. Without the spacer, it was fine.
With the 11 speed cassette without the spacer, the cassette couldn't be tightened up properly and was loose on the freehub and with the spacer, it was fine. It replaced a 11-32 Ultegra cassette which didn't use a spacer.