Some in-ground utility boxes have a large hole in the middle which could be a trip hazard. Where I work there is a ~70x150mm hole in the middle, right in the middle of the sidewalk. The safety person kept covering it with a pylon - again, dead center of the sidewalk… - so I made this to fill the hole. Printed in black PETG, it has so far survived over one full year in perfect shape including a 40°C summer,  a -20°C winter, and all the things that come with those on a commercial walkway.

This model is intended to be printed top down.

The design is overthought for a plug because I wanted it to be obvious and easily removable in a decade. The corner curves and funny shape on the bottom allows water to flow through even with debris build-up, and ice to form underneath and around it without lifting it up. The curved corners also make it easy to remove with a finger, and the ridges at those corners make it easy to pop out using a tool if the hole becomes packed with mud or ice.

You can also engrave something into the top simply by placing a negative space model on it in the slicer. For the original (the one in the photo) I put the company's logo on it. I didn't bother with a colour change to make it pop, but the texture of the PEI plate versus the texture of the bridged layer still makes it quite visible.

This is intended to fill a 70x150x50mm hole, which seems to be pretty common around here. If you need a different size, you can stretch the STL, or I've posted the f3d file if you really want - but be warned I didn't really design it for editing by others.