Abstract: A rotary assembly of a turbine stage of a gas turbine engine comprising a disc carrying internally air cooled blades around its periphery has a cover plate of one face of the disc to create a plenum for a cooling air supply to the blades. The cover plate is fitted to the disc by means of an annulus of bayonet connections at a first radius and is retained at a second radius, less than the first radius, by a split ring arrangement. The split ring is fitted into a groove in the disc and engages an inner rim on the cover plate to restrain axial movement. An anti-rotation key is engaged in a slot in the cover plate and in the disc and is also retained by the split ring.