What 2shot said... The 0550 and 0551 differ in the steel (S35VN and ELMAX respectively) and the pattern on the G10 scale (diagonal on the 0550 and horizontal on the 0551). Some of the early 0550's did use ELMAX steel, but I think those were very limited in number.
0560 is a bigger knife (longer handle and blade), has a flipper, and has 3-D machined G10 and titanium scales. The 0560 also uses the deep carry clip for all models (1st gen 0550's used the regular ZT clip, like on the 0200, 0300, 0350, and Skyline).
0560 is a bigger knife (longer handle and blade), has a flipper, and has 3-D machined G10 and titanium scales. The 0560 also uses the deep carry clip for all models (1st gen 0550's used the regular ZT clip, like on the 0200, 0300, 0350, and Skyline).
