A sturdy pencil case (based on the vault box) with locking nuts, available with 1, 2, 3 or 4 compartments. The inside length of 17cm should fit most pens, even a short ruler.

It's a print-in-place model, so no assembly required (except for the nut).

Tolerances are tight; you can try the tolerance test first. If it doesn't work, try lowering the flow ratio or try a slightly negative X-Y contour compensation (like -0.05).

I suggest printing the nuts (2 designs available) in a different color (I placed them on a different plate for that reason).