manhole rings 中文意思是什麼

manhole rings 解釋
人孔環
  • manhole : 人孔，（陰溝的）檢修孔；【鐵路】避孔。
  • rings : 吊環
  1. Directions for transporting and storing of concrete pipes, reinforced concrete pipes, prestressed concrete pipes and fittings and concrete manhole shaft rings

    混凝土管鋼筋混凝土管及預應力混凝土管管件和混
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