| 摘要 |
Adjustment risers for use in a manhole or catch basin, between a lower support structure, for example, a concrete riser, and an upper frame assembly, adjacent a surface in which the hole is formed, have a molded body and typically are annular; one or more ribs extend outwardly from a first sealing face and a corresponding one or more grooves are formed in an opposed second sealing face, each groove being in opposed relationship with a rib, whereby the adjustment risers may be matingly stacked to provide a required adjustment riser height for a specified manhole or catch basin.
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