The beads 21 are made of a stable material that maintains {HEAD ~ its physical properties} preferably over a wide temperature range and for {TAIL ~ a long life time} 
The beads 21 are made of a stable material that maintains { HEAD ~ its physical properties } preferably over a wide temperature range and for { TAIL ~ a long life time }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL OTH OTH OTH OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL