| 摘要 |
The manhole cover has a number of holes for introduction of a key for lifting the cover. Each hole comprises a cavity in the upper surface of the cover which consists of two portions (12,13) of different depths separated by a step (14). A cross-member (15) extends right across the mouth of the cavity at a point situated above the lip of the step. - The cross-member pref. has a recess (19) in one of its lower edges which lies opposite one of the portions of the cavity. The arrangement allows the manhole cover to be raised employing any one of a number of different keys (21) already in use.(2/3) |
