Abstract: A headjoint stopper for the headjoint of a flute includes a concave bottom disc member having an externally threaded stem axially extending from the back side, a deformable, ring-like sealing member positioned against the back side of the bottom disc, a clamping washing and a hex nut threadedly received on the externally threaded stem. The bottom disc member has an external configuration sized to fit the inside of the headjoint with metal-to-metal contact around the entire circumference of the bottom disc member. The externally threaded stem is integral with the bottom disc such that as the hex nut is advanced along the stem toward the bottom disc, the clamping washer is forced against the sealing member and the sealing member is thereby compressed between the bottom disc and the clamping washer.