I had previously stored these particular spools of thread in two little drawer units but each time I took one out to use, the rest fell over (which was annoying when it came to putting a spool back again) so I came up with this solution today using an old box file. I marked a sheet of paper with the spacing I wanted then used a stiletto to make holes through the paper and two layers of foamboard already cut to size. Lightweight plant support sticks were cut to length, one end dipped into PVA glue and then pushed into the foamboard. Melted wax was dripped onto the visible tips to round off the ends and prevent splinters.
As a thread storage system this might be considered fairly large but closing the lid will keep the threads dust free and the spools will no longer fall over and unravel. I’m delighted with it!