In fact, the cover is used to cover the road, he can avoid falling into the deep wells, of course, different materials to do out of the covers are not the same, in general, he has so few, like resin Covers, metal covers, etc., usually they are round. The use of covers is also great, such as in the pier, sidewalks or green belt are likely to use the covers. The covers are listening to his compressive and shock resistance is very good, so even if we used for a long time he would not have a damaged situation, and he did not have any value for recycling, so there would be no thieves to steal.

In general, the covers are playing a protective role in the unconscious of all of us play a protective role, so that we do not underestimate him.