go buy a thread file that has the TPI you want. Heat it red hot and let it cool slowly. Once cool it will have no temper. Use a 3 corner file and file each row of teeth so each row comes to a sharp point at one end of the teeth. After each row is finished. reheat the file to red hot then dunk it in a can of oil until cool, re-heat until a dark blu colour and dunk in oil again. File should now be hard enough to mark a pattern of lines on the hammer so you can finish up the diamonds with a small square file
