In {HEAD ~ this case}, the gap 23 is provided between the internal gear 3 and {TAIL ~ the iron ring} 22 as shown in FIG 2 
In { HEAD ~ this case } , the gap 23 is provided between the internal gear 3 and { TAIL ~ the iron ring } 22 as shown in FIG 2
OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH