Designed to provide an easy, clean installation of a 5mm LED in any wood, metal, or plastic surface.  The LED snaps into the holder, then the assembly is inserted into a 1/4" hole drilled into the mounting surface.  Add a couple of drops of CA, or hot glue (easier to remove with a heat gun), and it gives you a nice-looking way to add LEDs to your model.  Sold in sets of 5.