This design is a travel sewing kit design to carry everything required for a quick fix in a compact and robust format.
It is designed to contain: 3 buttons (less than 14mm), 5 to 10 needles, 2 safety pins, one needle treader (the head must be shortened), wire, one small blade and one printed thimble.
The thimble is 3D printed and must be minimalist to fit  inside the cap of the casing.
The blade is made by snapping off thin 30° (9mm) utility knife blades and gluing it to the printed handle (Exemple of blade:  https://www.amazon.com/Utility-Knife-Replacement-Blades-Multi-Purpose/dp/B0BRKB6DMZ?th=1).
To assemble the kit first load the buttons into the case body. Then roll the wire around the insert and secure it with the retainer. Place the knife, the safety pins, the needles and the treader into the insert and place all of it into the case body. Insert the thimble into the cap and screw it on.