This is just for Uppers
a) Stripped uppers- will need barrel, forward assist, hand guard, gas block, gas tube, charging handle, bolt carrier group + knowledge and skill to assemble
b) complete upper- still need, everything except forward assist
c) complete upper assembly- everything except bolt carrier group
d) complete upper assembly w/BCG- need sights of some kind (unless an A2)
From what I've read on the interwebz YMMV