I originally tried the one I remixed this from, but I didn't want to fill the big hole with plastic and/or solder. Using Tinkercad, I filled up the original hole and created a new hexagon with the required size. On the left, the original design with the round hole, on the right and on the knife, my remixed design. You may need to scale up or down the print depending on your printer settings because this is a tight fit. I used a hair drier to soften the plastic before pushing it in. PLA becomes really malleable even with a regular hair drier on the hottest setting.