Difference between disc and drum uprights

[shh120m]

Hi guys,

Just a guick one, whats the difference between disc and drum rear uprights?
The reason im asking is because iv got rear drums but i believe the driveshafts may be of the disc variant because they have a lip which doesnt allow them to pass through the sierra hub carrier, if you know what i mean. Forgive me if im talking bollocks but im sure i was told that the lip was only pressent on the disc sort. Im just curious and i dont want to buy the wrong set of uprights.

Thanks

Nathan