{HEAD ~ Lugs} and {TAIL ~ relief areas} formed on one face are staggered with respect to the lugs and relief areas formed on the other face 
{ HEAD ~ Lugs } and { TAIL ~ relief areas } formed on one face are staggered with respect to the lugs and relief areas formed on the other face
HEAD HEAD HEAD HEAD HEAD OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH