{HEAD ~ 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 {TAIL ~ a hold ring} for restricting movement of the seal ring in an axial direction 
is provided with
{ HEAD ~ 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 { TAIL ~ a hold ring } for restricting movement of the seal ring in an axial direction
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