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