| 摘要 |
A block plug comprising an opening (2), a central portion (3) positioned opposed to the opening (2) with a predetermined spacing from the opening and formed centrally of the opening (2), and an outer peripheral wall portion (4) covering an area between an opening end of the opening (2) and an outer periphery of the central portion (3) in a closed manner. The block plug closely contacts with an opened wall surface of a drain port (21) to enable blocking the drain port (21), and comprises a positioning fitting portion (7) which protrudes toward the opening (2) from the central portion (3) and is positioned coaxial with both of the opening (2) and the central portion (3).
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