By the way, I took joe's picture and marked it up so you can see the piece that's missing in the picture you posted. The fuse goes into the hole and the retainer slips over it, pushes down (spring tension holds it) and half turn fastens it in place. There may be horn or headlight relays for other vehicles that use the same method so you may be able to find one of those if you need one. Click on the image to enlarge it and see it better.
