I needed something quick to cover the bed frame bolts that were tearing into my mattress. I couldn't find anything so I whipped this guard up in Sketchup and thought someone might have an application for it.
I found that heating the bolt with a lighter for a few seconds and this screwed on and stayed nicely. I used it on a 6 mm bolt and a 14 mm nut but you could scale it, drill it or melt it a bit more to fit any size.
I printed it on low quality with no supports and it worked fine.