A capping unit (100) for articles such as containers and/or bottles in general, of the type including at least one capping group (3) bearing one or more capping heads (8) for screwing caps (6) or capsules on the articles moved by at least one transport line (4). It includes at least one capping heads store (19), adapted to retain a series of capping heads (8), in order to allow the rapid and automatic exchange and substitution of the spindles (25) of the capping group (3); the capping group (3) being moved by an associated motorization, up to reaching the store (19) such to store and pick up, automatically from the group (3) itself the suitable capping head (8) as a function of the size of the caps (6) or capsules to be screwed.