The "cups" are the outer race for the needle bearings---there are no retaining clips, but the groove will be there after you melt the plastic out. yes, you must reinstal the "cups", but they come as part of the new u-joint spider. Yes, go ahead and rebuild it---no different than the older style u-joints----its just that the automotive plants find it quicker and cheaper to use the plastic instead of metal retainer clips, on the assembly line.