A rotor is provided comprising a centre of mass and a rotational axis and a rotor sealing component extending circumferentially around the rotor for sealing between the rotor and a stator, wherein the centre of mass of the rotor is coincident with the rotational axis, and material of the rotor sealing component is not evenly distributed around its circumference. A stator sealing component in which the material is not evenly distributed around its circumference is also provided.