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