The channels are held together by one or more cross stringers which pass through sidewalls of each channel in apertures adjacent to a channel base and are secured to {HEAD ~ the channel base} by securing {TAIL ~ means} of various types 
The channels are held together by one or more cross stringers which pass through sidewalls of each channel in apertures adjacent to a channel base and are secured to { HEAD ~ the channel base } by securing { TAIL ~ means } of various types
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 OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH