An inner periphery of the socket is provided with a seal ring for sealing an interval between the inner periphery of the socket and an outer periphery of the plug in an airtight manner and a hold ring for restricting movement of {HEAD ~ the seal ring} in {TAIL ~ an axial direction} 
An inner periphery of the socket is provided with a seal ring for sealing an interval between the inner periphery of the socket and an outer periphery of the plug in an airtight manner and a hold ring for restricting movement of { HEAD ~ the seal ring } in { TAIL ~ an axial direction }
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