A simplified design of the original part in the picture. The part is designed to hold down the removable guard/vent/grid on top of the radiator.
Print with heat resistant plastic, because if there's no heat where it's supposed to be mounted, you probably have bigger problems than a broken or missing piece of plastic.
The design is split in half for easier printing so print two pieces but MIRROR ONE! Glue together or possibly rely on just friction with 3 pieces of filament through the built in holes for alignment and shear strength.
radiator-clamp.stl | 116.5KB |