Tuning (2nd) piece
2nd piece of a composed drone, slipped on the tuning slide of the butt piece; Used for tuning; Of smaller drones it is the outermost piece, sometimes provided with a bell.
Garvin, Wilbert: The Irish bagpipes: their construction and maintenance [Belfast 1978, Blackstaff Press]. Foreword by Breandán Breathnach. Kells, 1988 (2), p.2.