In accordance with yet another preferred embodiment, {HEAD ~ the first central area} has {TAIL ~ a diameter} which varies between about 1.8 to 3.7 mm, and the second central area has a diameter which varies between about 1.4 to 2.9 mm 
has
In accordance with yet another preferred embodiment , { HEAD ~ the first central area } has { TAIL ~ a diameter } which varies between about 1.8 to 3.7 mm , and the second central area has a diameter which varies between about 1.4 to 2.9 mm
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH