ยท? (drone stopper [Term not mentioned in available sources])
special plug used to stop [silence] the drone
Sliding plug or plunger inserted in the end of each drone, enabling to switch it on or off [during playing?].
Bibby-Wilson, Kim & Moore, Anne (eds.): Morpeth Chantry Bagpipe Museum: souvenir guide. Newcastle upon Tyne, 2003, p.9* (type only, no term).