When cocked, it rest on the tab formed on {TAIL ~ the flange} of {HEAD ~ a backwardly flanged mail door} 
When cocked , it rest on the tab formed on { TAIL ~ the flange } of { HEAD ~ a backwardly flanged mail door }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD