Since annular container flange 18 has {HEAD ~ a downwardly sloped upper annular surface} to act as {TAIL ~ a cam surface} and annular lower portion 38 is resiliently hinged, passage of annular lower portion 38 thereover is facilitated without the realization of great stress in annular frangible area 28 
Since annular container flange 18 has { HEAD ~ a downwardly sloped upper annular surface } to act as { TAIL ~ a cam surface } and annular lower portion 38 is resiliently hinged , passage of annular lower portion 38 thereover is facilitated without the realization of great stress in annular frangible area 28
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