The sun gear (3) is the center gear in the planetary set.
The ring gear (4) is the outside gear in the planetary set that is in constant mesh with the planet pinions.
The clutch packs (5), comprised of discs and plates, are used by the planetary transmission to control the power through the planetary sets. The inside teeth of the discs are held with the outside teeth of the ring gear and notches on the outside of the plates are connected with pins in the clutch housing. The pins keep the plates from rotating.