Because there are a number of ice makers that are compatible with my 29-year-old Sub Zero 550, there were differences that made it incompatible. My problem was to find one that came as close as possible. In particular the 'fill' bar provided that came with the unit I ordered was too long, but fortunately I was able to use the bar from the old unit. Other than that, the ice maker was fine and I'm back to making ice again