inner ring 12 may cause either structure by itself to be insufficiently strong enough to maintain structural integrity of a die cast end plate but spokes 18 greatly improve the strength of outer ring 11 by their connection to inner ring 12 for example spokes 18 retain outer and inner rings 11 12 in their proper relative positions by being embedded within the cast material thereby maintaining the proper position and integrity of retention structure 10 on rotor 4 as a result outer ring 11 is able to withstand the hoop stresses caused by resistance to outward radial forces being imposed on outer ring 11 by virtue of its embedded spoked attachment to integrally formed inner ring 12 an annular chamfer 26 is formed between radially inward surface 27 and axially inward surface 23 of outer ring 11 a pre casting structure is shown in fig6 shorting ring retention structures 10 see fig5 each have essentially the same outside diameter as lamination stack 30 so that outer perimeter faces 19 are essentially flush with outer surface 34 of lamination stack 30 in an exemplary embodiment a cylindrical mold having an inner diameter equal to or slightly greater than the diameter of retention structure 10 and lamination stack 30 and having an essentially planar bottom surface that is orthogonal to the center axis of such cylinder may be used for die casting rotor 4 in such a case a first shorting ring retention structure 10 is placed so that surfaces 21 22 abut the bottom mold surface and outer perimeter face 19 of retention structure 10 fits snugly against the inner walls.