The 60 series will fit in a 50 series. They are more "open" So if you replace the first one you will create a ledge going up to the second concave. So it works like this. You can replace n 3 by itself. If n2 is bad you have to replace n2 and n3. And if n1 is bad you have to replace n1,n2, and n3. Hope that helps.
