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