Someone wanted a “fresh copy” of the sun-bleached, paint-stained radiator knob they had.

So I scanned it, re-worked the cut-out in the middle and printed it.
If I had more skill, time and headroom, I would design one from the ground up, but I don't and this suffices for my needs.

I recommebd printing it in heat-resistant material (I used ABS), as the valve it controls can reach 80C (175F).

The 3MF file has the radiator button in 3 detail levels (simplify model), detailed in front and smoother in the back.
TBH, I can't really tell the difference…

The cut-out on the inside is 7.5mm and it's meant for a 6mm bolt.
However, you can simply plug the hole with a cilynder and cut out a new cube, to suit your needs.