Cryptex with a 6-digit numerical combination. The combination can be changed to any number 000000 - 999999, but only when the device is open.

Update: Added the reworked retaining ring file by Inglebard. For some users, the reworked version seems to work better.

Print the following:

1x tube_outer
1x tube_inner
1x ring_end
6x ring_inner
6x ring_outer

Make sure the ring pieces are laying flat and the tube pieces are laying on their larger ends during printing for optimal results. Supports recommended, though some pieces (especially ring_outer) have been successful without them.

Insert a ring_inner into each ring_outer with the notch aligned to the desired number. Slide each ring section onto the tube_outer with the notches aligned to the slot. Attach ring_end to tube_outer by inserting it with the smooth side facing outwards and one of the notches aligned with the slot. Turn ring_end clockwise to lock the assembly in place.

To close, insert tube_inner into the assembly and scramble the combination. To re-open, align the combination with the markings on tube_inner and tube_outer and remove tube_inner.