The first five hammers of each series are the most used of the Fretz Hammers. The only difference is the size of the hammers for the scale of the work. Jewelers should start with the HMR-1 thru 5 Set. Metalsmiths who forge and form heavy stock will pick up one of these larger hammers in the HMR-101 thru 105 Set. Those working on very small metal work will appreciate the scale of the HMR-401 thru 405 Set.