In a spiral groove bearing a gap between a surface portion which has grooves thereon and its opposing surface portion is smaller than {HEAD ~ the gap} between {TAIL ~ any other surface portion} which does not have grooves thereon and its opposing surface portion 
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In a spiral groove bearing a gap between a surface portion which has grooves thereon and its opposing surface portion is smaller than { HEAD ~ the gap } between { TAIL ~ any other surface portion } which does not have grooves thereon and its opposing surface portion
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH