a printing element having an impacting surface at {TAIL ~ its front end} and {HEAD ~ a driven surface} at its rear end 
a printing element having an impacting surface at { TAIL ~ its front end } and { HEAD ~ a driven surface } at its rear end
OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH