The Cokin Gradual ND Kit (H300-02) contains: the ND2 filter (P121L) with 1 stop density and hard edged transition; the ND4 filter (P121M) with 2 stop density and hard edged transition; and the ND8 filter (P121) with 3 stop density and soft edged transition.
Neither a P-series filter holder nor an adapter ring, the diameter of which will depend on which lens you are using, is included in this kit.