Tuning device of the drone(s), allowing the pitch of a drone to be raised by a tone; In a set of 4 drones, only the 2nd largest drone has a tuning bead, allowing a standard 3 drone harmony for music written in G or D; According to the internet source, "More complex drones have at least one tuning bead on each drone", which appears to be an odd statement, because it is difficult to visualise a drone with multiple tuning beads...