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