Tom Gardner Mars@Tacks fired this volley in
:

I hate this set-up! I just don't trust it
not to slip but I can't think of a better way of locking the part on the
shaft yet be able to adjust it easily.

Make a couple of flats! They won't compromise the strength, and will
ensure (if the screws are gum-locked) that there's no slippage.

If you 'dimple' instead of flatting, there also will be no longitudinal
play.

They make shaft-mounted stones for a reason! G

Lloyd