Fulcrum racing 3's shimano hub

SteveR_100Milers

have fitted a 10 spd cassette to the rear wheel, which is 8/9/10 spd compatible, the hub looks like no shimano hub (FSA aswell) as the splines are smoothed out towards the hub centre. I wasn't sure that the spacer ring you need for the 10 spd cassette was required, but stuck it on assuming it is, although there appears to be a huge gap between the spokes and the cassette, much more than that on the FSA and shimano wheels I have - is the spacer required? Without it, the cassette is loose on the hub, even with the lock ring done up tight.
I cant tell until new tyres arrive then i can stick them on the bike and try it out.