A mounting device for coupling two rotatable elements is provided. Specifically, a device for mounting a machine element onto a shaft, and in particular for mounting a narrow machine element on to a shaft, is provided. In one embodiment, the device includes a radially deformable inner sleeve that cooperates with an outer sleeve. A locking nut threads onto the inner sleeve to displace a thrust plate toward the outer sleeve so that the machine element is clamped between the thrust plate and the outer sleeve. In another embodiment, the device includes opposing pairs of inner and outer sleeves having mating tapered surfaces to provide axial clamping force and radial clamping force. The machine element is axially clamped between the pairs of inner and outer sleeves.