The grid patterns, or raised studs, on the manhole covers not only enhance skid resistance, but also allow drainage workers to identify two kinds of manhole covers.
The grid patterns, or raised studs, on the manhole covers not only enhance skid resistance, but also allow drainage workers to identify two kinds of manhole covers.
The grid patterns, or raised studs, on the manhole covers not only enhance skid resistance, but also allow drainage workers to identify two kinds of manhole covers.
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