| 摘要 |
An improved manhole structure is disclosed which comprises a cover having a rim inclined inwardly at 45 DEG , on which a plurality of protrusions are provided; a ring for elevating the cover, having an upright inner wall and outer wall and an upper face and lower face, both inclined inwardly at 45 DEG , on the said upper face a plurality of holes are formed for engagement with the protrusions formed on the cover, and on the said lower face a plurality of protrusions are formed; and a base having an upper surface inclined inwardly at 45 DEG , and a flat lower face, on the said upper surface a plurality of holes are formed for engagement with the protrusions formed on the lower face of the said ring.
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