A container originally designed to hold my emergency medication and small enough to be kept on a keyring. The OpenSCAD source code is included to help customisation but requires the BOSL2 library for the threading and textures.

Please be aware that this was designed for my personal use and I am releasing it in the hope that it may prove useful for others but use at your own risk. These aren't airtight and some materials may still let moisture in so if you use it for storing pills then make sure that they aren't prone to deterioration when exposed to air or moisture or out of their original packaging for significant periods of time. Of course, it can be used for other things too. 

It is designed in 3 parts. The 2 parts that make up the cap need a tight tolerance and can be difficult to push together but I place the cap over a hex socket, put the ring holder into the cap and tap it into place with a smaller hex driver and a hammer. Then fit a 5mm stainless steel ring through the hoop.

The slop parameter is somewhat printer dependent and determines the interference between the threads. There is a model somewhere that can be used to determine this value for a printer but I've lost track of it. If the thread is too tight then increase the value slightly. BOSL2 makes the gap between mating parts of the thread as 4x this value so adjust it in small increments.

The thread shouldn't be too loose and can be tight when first printed but gradually working it will help to keep it a nice tight fit without making it insecure. Tighten and loosen it in small increments, gradually working your way until it is fully closed. I've used mine for over a year with no issues.

The STL file (as exported by OpenSCAD) includes all 3 parts so needs to be split into 3 objects in the slicer (the button with a large O on it at the top in Prusa Slicer). The cap then needs flipping.

I've printed mine in PLA on a Mini+ with a 0.25mm nozzle and a layer height of 0.1mm. A printer file is included with these settings.