said {TAIL ~ core} having a central axis which coincides with said axis of said surrounding {HEAD ~ ferrous cylindrical case}, 
said { TAIL ~ core } having a central axis which coincides with said axis of said surrounding { HEAD ~ ferrous cylindrical case } ,
OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH