wherein the metal is selected from the group consisting of: {HEAD ~ cobalt}, {TAIL ~ nickel} or chromium, and a metal alloy of these metals 
wherein the metal is selected from the group consisting of : { HEAD ~ cobalt } , { TAIL ~ nickel } or chromium , and a metal alloy of these metals
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH