Thereby, {HEAD ~ the step difference} of {TAIL ~ rigidity} is decreased while further raising the rigidity, the shearing stress is alleviated, and the bead part durability is enhanced 
Thereby , { HEAD ~ the step difference } of { TAIL ~ rigidity } is decreased while further raising the rigidity , the shearing stress is alleviated , and the bead part durability is enhanced
OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH