| 摘要 |
PROBLEM TO BE SOLVED: To provide a resin-made in-core easily and inexpensively manufacturable, having high earthquake resistance, and not corroded by rust. SOLUTION: The inner peripheral surface is provided with a groove 11 for a seal ring from an opening 12 side, and a groove 15 for a breakaway preventing ring continuously having a tapered surface 13 of which the diameter gradually expands from the opening 12 side to the back side and a circumferential surface 14 substantially parallel with the axial line at a position on the back side separated from the groove 11 for the seal ring. The resin-made inner core inserted into the end of an insert hole 9 inserted from the opening 12 side of a socket 10 of an olefin based resin-made breakaway preventing joint in which a seal ring 20 is mounted in the groove 11 and the breakaway preventing 18 is mounted in the groove 15, is manufactured of resin having tension elasticity of 1000 to 4000 MPa, for example polyacetal.
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