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