{HEAD ~ An extruded aluminum channel} is formed with {TAIL ~ a wide central T shaped groove} and narrower outer T shaped grooves transversely spaced on opposite sides of the central groove 
{ HEAD ~ An extruded aluminum channel } is formed with { TAIL ~ a wide central T shaped groove } and narrower outer T shaped grooves transversely spaced on opposite sides of the central groove
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH