Sigh. Can’t get 12 sp Shimano cassette to sit on DT 240 hub properly

I’ve put a new SLX cassette on my hub, but it’s not sliding on properly. When I go to screw the lockring on it only does a turn or two before sticking. I’ve had similar before and the problem is clearly the cassette not seating properly or some of the individual cogs being squint…

But there’s nothing between the cassette and the hub except one tiny plastic squeak spacer, and all the cogs seem aligned..

I can squeeze my little finger between the spokes and the cassette, but on my other wheel, with the cassette seated properly I can’t.

So it seems like the problem is in the hub or the interface between it and the cassette, but I can’t see where…

Help!

I forget which one, but either the 11th or 12th cog can go on 180 deg out, and so doesn’t seat properly which would cause the issue you’re having.

What SOM says. It’s likely to be the final two cogs not being aligned properly. They have small dots on one tooth of each cog that you use to make sure it’s lined up properly.

Hmmm, cheers guys. I’m not convinced it is that, as the main chunk of big rings seems further from the spokes than on my other wheel.  ( I have aligned the dots as you suggest)

Anyway, I’ve put it all back together and the gears are all to shit so looks like it is in the wrong place.

You definitely have the right cassette for the freehub body? Have you tried the outer cogs in different positions? Might need them to push it all on and sit in place.

Is the free hub body old and a bit chewed up by the old cassette, 2 minutes with a file will sort it out and stop the sprockets hanging up if it’s that