I created this model for capping the cut ends of 3030 aluminum extrusion bars. I used the 3030 bar material for a roof top solar panel mount. The caps simply tap into place with a rubber mallet, or hammer with a scrap of wood to protect the cap surface. There may be a retail product for this, naturally they would not be this economical, convenient or as cool as printing your own.

I made these caps for a very snug fit. Deburring the cut end of the aluminum may be required, especially if the cut is rough. The cap can be scaled in the x, y and or z axis using most slicers for a custom fit. For example, in Cura select the model then select scale then deselect uniform scaling. Pulling the x,y, or z axis will cause the model to scale in that direction only.

ABS or ASA are good materials for this model. ASA being more resistant to sunlight.