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