This is a 1/4" hole centering jig used to find the center on the edge of a boards so that you can drill matching holes to join edges of wood together using 1/4" dowels.
Place the pins straddling down over the edge of both sides of the board. Rotate until both pins are firmly on the side of a 1/2" to 3/4" board. The 1/4" hole can be used as a guide for a 1/4" drill bit to drill a centered hole for dowel. Align to opposite board and repeat.
Using a drill-stop collar will help ensure you have consistent depths.
YouTube video of similar tool: https://www.youtube.com/watch?v=B-gy1iIZu_w
0.25in_Center_Jig.stl | 382.8KB |