area of the perforations is typically 40 of the ring 39 s surface area the rings 502 and their base portion 504 may be made as a single diametrical element or in pie shaped segments as seen in fig3 forming a diametrical disk the rings 502 and their base portion 504 may be provided as one piece diametrical rings forming concentric circles and attached to the stator base plate 44 via dowels 41 as illustrated in fig2 the rings 502 and base portion 504 as seen in fig3 may also be furnished as segmented rings necessary only if they are to be heat treated to improve wear resistance in which case a series of pie shaped concentric ring segments as seen in fig3 forms a wedge or pie shaped segment for attachment to the stator plate 44 shown in fig2 a row of teeth segments 605 as seen in fig3 may also be integrated into the pie shaped segments shown in fig3 or as a one piece diametrical concentric ring and also attached to the stator base plate 44 these teeth segments 505 are cooperative with the rotor tooth segments 604 illustrated in fig3 the rotor illustrated in fig3 may also be made in.