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