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.

Note: the high temperature of the radiator can cause the model to deform when using certain materials. You can counteract this by printing with a larger infill, by increasing the thickness of the item, by using stronger materials.

This version (rounded) was based on my first version and Ken Cooper's idea about edge rounding.
https://www.thingiverse.com/thing:3339046
https://www.thingiverse.com/thing:3339628
The rounded version appears to be nicer and stronger.