I have been experimenting with my Lyman and find that it likes a flint that is 1/2 inch in lenght by 3/4 inch in width.The flint at its thickest part should not exceed 1/4 inch.Mine works best with the bevel up.I have been using Rich Pierces flints, and have made a few of my own.With the above described flint I have considerably lenghtened my flint life and get good ignition.I wrap the flint in lead, but I have another lock that uses leather with good results.