{HEAD ~ a cylinder} with two independent, opposing shafts that assumes {TAIL ~ two characteristic positions}: 
{ HEAD ~ a cylinder } with two independent , opposing shafts that assumes { TAIL ~ two characteristic positions } :
HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH