Once you find exactly what size flint works best in your rifle you need a way to make sure you buy just that size. I came up with an idea that works good for me. I took the plastic lid off a coffee can and cut a piece the size of a credit card so it fits in my wallet. Next I layed out the top and side profile of the perfect flint size for my rifle on this card. I cut these profiles out on the card and now I always have a guage with me when I find flints for sale. If you have more than one rifle you can get more than one template on a card if you lay out carefully.