As shown in FIG 20, the section of the inner ring 153 is shaped like a fallen L and the section of {HEAD ~ the outer ring} 152 is a rectangle seated on the L shaped section of {TAIL ~ the inner ring} 153 
As shown in FIG 20 , the section of the inner ring 153 is shaped like a fallen L and the section of { HEAD ~ the outer ring } 152 is a rectangle seated on the L shaped section of { TAIL ~ the inner ring } 153
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH