I replaced one control arm with a moog #k7424.
Those are now sold out but they have #ck7424 and rk7424.
What are the differences? The descriptions both say, complete control arm with ball joint. I'm thinking they updated the part and these are the new numbers?

 

rk is their mid range r-series

ck is their problem solver line, you want this one.

Id imagine the main difference is the grade of balljoint and possibly bushings.