One rubber portion can be, for example, {TAIL ~ the central core} of the rubber thread, while a second rubber portion can be a jacket surrounding {HEAD ~ the central core} 
One rubber portion can be , for example , { TAIL ~ the central core } of the rubber thread , while a second rubber portion can be a jacket surrounding { HEAD ~ the central core }
OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD