Jazz I do have a fancy SKF locknut with a grub screw (pricey little bugger) which I could use, the only issue is accessing the grub screw as it's on the side. The cap / bolt is easier, as I can bolt it up from the top, but proper preload doesn't guarantee the bolt staying where it should without threadlock (I think).

As for expansion John, I'm guessing you meant thermal expansion, which would force the housings further apart and increase the preload? this shouldn't be an issue as all the parts will stay close to room temperature all the time.

Regards,
dsc.