RJ45 Dust Cover Plug

If you break off the handles they even work as a port lock.

I printed them in PETG with a 0.6mm Nozzle and they fit pretty well. You'll have to use Flush-Cutters to cut them out of the grid or sand off the edges.

If you want to print many of them simultaneously, I added some alignment-marks at the corners of the 2x2-Grid