The block usually includes a plurality of interconnected gas containing tunnels or passages which form a closed loop path in {HEAD ~ the shape} of {TAIL ~ a triangle}, a rectangle, or any polygonal path 
of
The block usually includes a plurality of interconnected gas containing tunnels or passages which form a closed loop path in { HEAD ~ the shape } of { TAIL ~ a triangle } , a rectangle , or any polygonal path
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH