Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:1335416.
Center Marking Tool for woodworking. Created in Tinkercad and printed on DaVinci Jr.
Designed to fit 7.5mm diameter pencil. I used one from Home Depot.
This tool is very handy and makes it quick and easy to mark a centerline on a board. It will fit over many size boards including the wider part of a 2x4. The pencil fits tight so it holds in place while you drag it across the board.
See more detail here: https://youtu.be/vG-LGR2Q4NM