I'm upgrading my bike from 8 speed to 10 speed.

The rear hub is a Shimano 8spd cassette compatible Edco.

I have purchased a 10spd Shimano XT cassette. It fits onto the freehub body's splines. With no sprockets the lock-ring can be threaded on 3 full turns.

However when I tighten the lock-ring the sprockets are still a bit loose.

Investigation shows that the smallest sprocket is tight to the free-hub body (as the cutouts that fit the splines do not run all the way through the sprocket). This allows the lock-ring to engage 2 & 1/2 turns.

Fitting a 1mm spacer under the largest sprocket removes the sprocket looseness BUT means the lock-ring only engages 1 & 1/2 turns, probably not enough for durability (did I mention this is a tandem with a combined crew weight of 150kg that likes to stand on the pedals up hill). I'd be happy with 2 & 1/2 turns plus tight sprockets.

The ideal solution would be thinner spacer (I need to measure the lock-ring thread pitch to figure out exactly how thick) but I can't find any.

Any thoughts or other possible solutions.

D