For six string CAM guitar tremolos, you'll need only two springs... either a standard tension set or a heavy tension set, depending on the string set used. String sets containing strings sizes between .008 and .048 must use these standard tension springs. If any string is larger than .048, you must advance to the heavy springs to compensate for the extra pull. Sold individually.
FYI: So you don't do the whammy thing anymore eh? Whammy Parts has a new CAM lock that will turn your Kahler guitar or bass tremolo into a fixed bridge. Chuck those springs... now you can drop tune with a simple twist with your fine tuners. Only $12 (same as 2 springs), see CAM lock clip #8411.