The 3D printed version of the maracas uses magnets to hold the two halves together.
Insert the magnets into the three magnet slots on the maraca half. You may want to add a dab of glue to the slots if your tolerances are loose.
To ensure that the other maraca's magnets are a matching polarity, attach magnets to the slotted magnets. Mark the side of the magnet that is facing up with a marker.
Secure the marked magnets into the other half of the maraca. Make sure to insert the marked side of the magnet facing down in the slots.