| 摘要 |
PROBLEM TO BE SOLVED: To provide a base seat for a protective cover for a riser for inspection in a subsurface drainage conduit which can be easily installed to be concentric with the riser, and which will not move to the riser. SOLUTION: In this base seat for a protective cover, plural protrusions are provided from an inner circumferential surface of the circular base seat inward, and inner end surfaces of the protrusions are on a concentric circle with the inner circumferential surface of the circular base seat in such a way as to be engaged with the riser. At least three protrusions are provided roughly at a constant interval along the circle, preferably.
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