99 xc70 exhaust question
 

I have a question on the dual exhaust. I have a99 xc70 which I am going to put the R double in but the part numbers 8631696 end pipe and
9470988 end pipe says they both have been replaced by part number 30681851. But I see that on the dual one side is smaller than the other so how can both parts be replaced by one? I am sort of new to volvo so am I missing something?