{HEAD ~ The apparatus} 2 wherein said {TAIL ~ protective coating} is selected from the group consisting of cobalt alloys, nickel alloys and tungsten carbide alloys 
wherein
{ HEAD ~ The apparatus } 2 wherein said { TAIL ~ protective coating } is selected from the group consisting of cobalt alloys , nickel alloys and tungsten carbide alloys
HEAD HEAD HEAD HEAD HEAD HEAD OTH REL OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH