A rotor for mounting blades thereon to form an impeller rotatable about a main axis thereof. Each of the blades has a mounting portion. The rotor includes primary slots and auxiliary slots, each of the primary slots is adapted for receiving the mounting portion of the blade. The primary and auxiliary slots are adapted to change their dimensions during rotation of the impeller due to centrifugal forces and thermal effects caused by the rotation thereof. The change in dimensions is adapted to exert pressure on the mounting portion of the blade to retain it within the primary slot.