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