Each carriage has a rearwardly projecting tongue, slidably received in a slot formed in {HEAD ~ flange structure} on {TAIL ~ the port plate} 
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Each carriage has a rearwardly projecting tongue , slidably received in a slot formed in { HEAD ~ flange structure } on { TAIL ~ the port plate }
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 TAIL