According to {TAIL ~ one aspect} of the invention, {HEAD ~ the coiled central section} of the spring is made harder than its ends 
is made harder than
According to { TAIL ~ one aspect } of the invention , { HEAD ~ the coiled central section } of the spring is made harder than its ends
OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH REL REL REL REL OTH OTH