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