The size part is easy. Get a flint for it that is as wide as the widest part of the frizen. As to the type, get the kind that makes the most sparks in the pan. At about $1.50 per flint you can experiment with the four or five kinds that are available. If none of them seem to do the trick, maybe the problem is in the frizen. It may need hardening or replacing or resurfacing. Do a search on these forums and you'll get more than enough ideas of where to look for your problems and the solutions for them.
