Central tightening nut loose on my DirectStream toroidal transformer

Had the hood open today on my DS Dac, to upgrade the fuse.

Had it in my head I’d read a post on here with someone having a loose nut on their DS’s toroidal TX?
Thought to check mine when I had the chance and yup, mines was loose too.

An 1/8th turn got it finger tight, but noticed it lost the grip when nudged slightly?
It wasn’t the nut tightness, it was the central threaded bar that was rotating, with the nut in tow.

A finger tighten fixed it again, decided to leave it be and put the lid back on.

There’s no hum or ground issues of any kind with my dac, but wonder why and how this could be happening?

Is there a clamp point on the underside of the casework for this TX threaded bar, that I need to work with to get it clamped tight?

Seems OK after finger tightening it again,
But just thinking in terms of any potential vibration (at least ion paper) affecting performance?

Maybe not even an issue, just seems odd when nut/threaded bar was rotating on itself., thought I’d ask.