13x13mm chipboard(18mm) socket.

thingiverse

If you've ever managed to punch a hole in chipboard, you know just how messy it can become. One of the major issues is fragmentation over time, leaving behind a multitude of small pieces that look absolutely awful. So I came up with this solution - a fitting that perfectly fills a 13x13mm square hole and effectively covers any chipped edges. It also features a clip at its rear end, which can easily snap into place on an 18mm chipboard.