Hey Jezza,

Can you use a thin file and correct the thread? As in if you can get the nut on halfway, you must have damaged the thread on the pitch whist removing the turbo possibly?

Try and find where it is damaged, clean up the thread, then use the nut with a good helping on anti seize and work the nut up and down a few times til you get it on all the way.

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Cheers,

Simon.