This is a support pin as found on adjustable shelving. Usually when you get a bookcase or some furniture it comes with extra pins. For some reason I can never find those extra pins when I need them.

These printable pins work well as a replacement and they're quite small so you can print a handful of them in an hour.

These are designed to fit my bookcases and provide a snug fit in the 0.185" holes. The peg diameter as described in the STL file is actually 0.19" which I discovered by experimentation provided the best fit for my printer and shelves.

The image with the blue background is a rendering of the model to give a better perspective on the shape.

I printed these with support at 0.25mm layer height and 100% fill. It's possible that another orientation would allow printing without support, but I haven't tried.