I believe all the 550's are the same. For instance the difference between a 550B & a 550C is how the ram link arms are fastened to the press. Every time Dillon makes a change they seem to change the letter.So I guess what I'm trying to say is yes they will work. If it says "for 550" it will work on all 550's.I have a 550B set up for large primers & a SDB set up for small primers and it is a fantastic set up.No changing, just sit down & start pulling the handle!!!! I do have one problem, a couple of weeks ago I picked up another 550B.for a great price ($245.00).I'm thinking about setting it up for .30-30 Winchester.