Before printing, you should take measurements of your radiator.
Details of the measurements - in the pictures.
In the Customizer you should change values for variables "diameter" and "distance".
You can leave the values of other variables unchanged.
The hook should be mounted tightly on the radiator.
It is mounted by pressing it with force - until it clicks and locks.

Update: 2019-01-08.
There is a second version of the object that has rounded shapes.
https://www.thingiverse.com/thing:3342912
That version is based on Ken Cooper's idea about edge rounding.
The rounded version appears to be nicer and stronger.