I use a lot of 3mm (diameter) x 3mm (height) cylindrical rare earth magnets to hold 3d-printed puzzles and models together. The magnets can be hard to work with-- they are too small to comfortably grip, and it often takes some force to get them to fit into the holes on the model.

These tools solve the problem:

• include a 3.2 mm (dia) x 3.2 mm (height) cylindrical recess in your CAD model
• load the + or - tool with a magnet (the correct orientation will stick)
• add a little JB Weld epoxy to keep the magnets in place for the long run
• insert magnet into your model using the comfy handle
• done!

This tool was developed as part of the project `Motivating First-Year Calculus with Robotics' supported by the National Science Foundation under DUE-12-45540. For more from this project, see my webpage.

Just print and go! Be sure that you insert the magnets into the tools with the correct side out. The two tools should stick together if you've got them correctly inserted.