I'm glad you liked my idea, and a folding ring sounds like a great solution. I'm not sure what the inside dimensions are, but besides a fire starter kit, I bet they would make outstanding pre-measured load tubes for hunters. Infinitely more PC than the plastic ones used nowadays, and way cooler on top of it. Also, a lot of engraving opportunities for customers to personalize if they wanted to, charge size data on the outside with a corresponding hash mark on the inside, different game animals, etc.