Just picked a couple of these up and knew that they needed inserts.
All are half the height of the respective drawers and have a 0.2 margin.
The middle drawer rear tray is notched for the magnet rivet. The lower rear tray is below the rivet in the one I am using.
The front tray is sloped for easy removal of objects.
The sides are keyed for the drawer slides and marked Right and Left.
When inserting the middle third, do it before the last tray, the tolerances are snug with the magnet pin. The middle drawer pin will “Snap” into the tray, it can be used solo.
The author marked this model as their own original creation.