Hi Vinnie
The slit in the side obviously contains part of the thread so when the two sides are squeezed together by the screw, it distorts the ring and grips the thread on the shaft. It works very well but as I mentioned in an earlier post, I did use an impact screwdriver to make sure that the locking screw is properly tightened. It doesn't have to be hit hard, just tapped to ensure that it's a bit tighter than you can do with an ordinary screwdriver. A locking nut is a good idea for peace of mind if you can get one over there.
Stuart - good idea about the hoseclip. A handy quick-fix but I'd mark the securing ring in some way so that you can see it's not slowly undoing itself and easing the hoseclip off!!!