These caps are useful to fit to steel angle stock if they are being stored in a place where the cut ends could cause damage or injury.
I have made and tested models for sizes I had in stock:
To modify for other sizes, the original designs are at: https://www.tinkercad.com/things/9nhtK8HVY0N
Print with 100% infill and 3-4 perimeters depending on nozzle diameter.
A stiff TPU or TPE works well. PETG is also suitable but not as impact resistant.
They should push-fit firmly; if the fit is loose then make a small + XY size compensation in slicer.
The author marked this model as their own original creation.