Yep, the hex bit on the end is effectively a lock nut for the threaded sleeve that sets the spring tension inside the knurled handle, can come undone...
If it's this one, put some decent tape around where the end cap meets the main part of the handle, there's a threaded sleeve inside that acts on the...
funny it was Avs dad, as I stole this idea from Billie fuller 's Dad. who had let us use their own at Teretonga a few years ago.
I couldn't find one...