{HEAD ~ The surfaces} of oxidation films 13a, {TAIL ~ 13b} are mirror finished if necessary 
of
{ HEAD ~ The surfaces } of oxidation films 13a , { TAIL ~ 13b } are mirror finished if necessary
HEAD HEAD HEAD HEAD HEAD HEAD REL OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH