A fan rotor assembly for a gas turbine engine, the assembly comprising: a rotatable shaft; an annular sleeve (30; 130) having an inner member (34; 134) connected around the shaft to rotate together therewith and having an outer member (36; 136) with a first end connected to the inner member (34; 134), the outer member (36; 136) being located outwardly spaced apart from the inner member (34; 134) and the inner and outer members (34, 36; 134, 136) being concentric and radially spaced apart from one another, the outer member (36; 136) defining an annular continuous frustoconical inner surface (46; 146) angled such as to extend closer to a central axis of the rotor assembly near the first end than away therefrom; a rotor having an annular disc (50; 150) having an enlarged outer perimeter portion on which are supported a plurality of blades extending radially outwardly therefrom, with the sleeve (30; 130) and disc (50; 150) being axially movable relative to one another, the disc (50; 150) including an annular protuberance (60; 160) extending radially inwardly of the outer member (36; 136) and forced toward the first end, the protuberance (60; 160) having a continuous frustoconical outer surface (64; 164) complementary to the frustoconical inner surface (64; 164) of the outer member (36; 136) and in torque-transmitting engagement therewith, an annular gap being defined between the shaft and the disc (50; 150) and the disc (50; 150) being spaced apart from the inner member (34; 134); and means for axially pressing the sleeve (30; 130) and the disc (50; 150) against one another to maintain the protuberance (60; 160) in forced engagement with the outer member (36; 136) and the complementary frustoconical surfaces (46, 64; 146, 164) in torque-transmitting engagement with one another, characterised in that: the inner and outer members (34, 36; 134, 136) are connected by a radially extending wall (38; 138); the annular disc (50; 150) has an annular recess separating the enlarged outer perimeter portion from the protuberance (60; 160); the outer member (36; 136) of the sleeve (30; 130) is received in the annular recess of the disc (50; 150); and the insertion of the protuberance (60; 160) inwardly of the outer member (36; 136) of the sleeve (30; 130) is resisted only by the interference between the complementary frustoconical surfaces (46, 64; 146, 164). a rotatable shaft; an annular sleeve (30; 130) having an inner member (34; 134) connected around the shaft to rotate together therewith and having an outer member (36; 136) with a first end connected to the inner member (34; 134), the outer member (36; 136) being located outwardly spaced apart from the inner member (34; 134) and the inner and outer members (34, 36; 134, 136) being concentric and radially spaced apart from one another, the outer member (36; 136) defining an annular continuous frustoconical inner surface (46; 146) angled such as to extend closer to a central axis of the rotor assembly near the first end than away therefrom; a rotor having an annular disc (50; 150) having an enlarged outer perimeter portion on which are supported a plurality of blades extending radially outwardly therefrom, with the sleeve (30; 130) and disc (50; 150) being axially movable relative to one another, the disc (50; 150) including an annular protuberance (60; 160) extending radially inwardly of the outer member (36; 136) and forced toward the first end, the protuberance (60; 160) having a continuous frustoconical outer surface (64; 164) complementary to the frustoconical inner surface (64; 164) of the outer member (36; 136) and in torque-transmitting engagement therewith, an annular gap being defined between the shaft and the disc (50; 150) and the disc (50; 150) being spaced apart from the inner member (34; 134); and means for axially pressing the sleeve (30; 130) and the disc (50; 150) against one another to maintain the protuberance (60; 160) in forced engagement with the outer member (36; 136) and the complementary frustoconical surfaces (46, 64; 146, 164) in torque-transmitting engagement with one another, characterised in that: the inner and outer members (34, 36; 134, 136) are connected by a radially extending wall (38; 138); the annular disc (50; 150) has an annular recess separating the enlarged outer perimeter portion from the protuberance (60; 160); the outer member (36; 136) of the sleeve (30; 130) is received in the annular recess of the disc (50; 150); and the insertion of the protuberance (60; 160) inwardly of the outer member (36; 136) of the sleeve (30; 130) is resisted only by the interference between the complementary frustoconical surfaces (46, 64; 146, 164). the inner and outer members (34, 36; 134, 136) are connected by a radially extending wall (38; 138); the annular disc (50; 150) has an annular recess separating the enlarged outer perimeter portion from the protuberance (60; 160); the outer member (36; 136) of the sleeve (30; 130) is received in the annular recess of the disc (50; 150); and the insertion of the protuberance (60; 160) inwardly of the outer member (36; 136) of the sleeve (30; 130) is resisted only by the interference between the complementary frustoconical surfaces (46, 64; 146, 164).