This is an insulator/spacer that sits in the wall bracket to allow the radiator to expand and contract without making a noise or damaging either the radiator or bracket, every time I remove a radiator to decorate the spacers are in two pieces.
So I measured up an original and designed a new one, for reference the originals are blue and the new one is grey
I did a test print in pla but I suspect petg would be better
The author marked this model as their own original creation.