This cap is designed to be tapped into place over the end of a piece of rebar to make it more visible, and more difficult to hurt one's self on.

This is embossed with the burning man logo, available in the OpenSCAD Burning Man Logo library found here: http://www.thingiverse.com/thing:30094

The design is only parametric in that you can adjust for the size of rebar you're using. Changing other variables may break the design.