If you have a sprinkler system then you see some of these in your yard. Better yet, I bet you have chopped a few up with the lawn mower or had the dog eat one or two! The are valve covers and are a part of your sprinkler system. The green lid is a top for the total valve box that protects the valve underground. They are very important and you need to make sure they are clear and easy to find. The valve box keeps dirt and other debris from covering the valve up. This matters most when you go to perform maintenance on your sprinkler system. If they are covered up and start to have issues it could get pretty costly trying to use a locator to find them all. We buy ours at Ewing Irrigation & Landscape Supply on Lynbrook Ave. Hope this helps!