said inside end of {HEAD ~ each} of said {TAIL ~ pole pieces} being a concave, curved, inside cylindrical surface which is shaped and sized to conformingly mate with said outside surface of said ferrous cylindrical wall, 
of
said inside end of { HEAD ~ each } of said { TAIL ~ pole pieces } being a concave , curved , inside cylindrical surface which is shaped and sized to conformingly mate with said outside surface of said ferrous cylindrical wall ,
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH