I want to share this ultra simple case for filters, step-up rings or even lenses. It can be made of paper, cardboard, leather or any other flat material. I used a heavy art paper, as it is easy to cut but stiff enough to give a litte protection.
The pattern is self-explanatory. If one wants to adjust the size, scale the hole drawing to match the diameter first, then adjust the hight. If one cuts it by hand he may ignore the little wings and use some tape instead of glue.
Hook-and-loop tape works fine for the lock, but you may find something more dressing (especially for leather).