This is a customizable machine screw cover.  It is useful when there are burrs on the head of a fastener as it protects items nearby.  

The STL file is for a 10-24 square head (Robertson) machine screw.  It was initially used in an accordion case.  

The part was generated using OpenSCAD so you can tweak it for another fastener.  There is an option in the design file to have a pin inside the head or not.  This pin helps secure the cap on a square head screw.  A little Shoe Goo was added to hold the part in place.  This part was printed with PLA.