{HEAD ~ The rings} are preferably formed as {TAIL ~ open cylinders} having a series of axially extending slits through the wall thereof 
are preferably formed as
{ HEAD ~ The rings } are preferably formed as { TAIL ~ open cylinders } having a series of axially extending slits through the wall thereof
HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH