Protector that screws onto bottom of 1/2 - 13 screws
R1 is modeled based on Fusion360 screw profile, while R2 is modeled by "hand" with extra clearance IIRC. R1 may need to be stretched in the X/Y directions, depending on your printer.
As seen in this video: https://www.youtube.com/watch?v=HGflbBo4Eok