dura 15 in. x 21 in. x 6 in. deep extension valve box in black body green lid dura <p>use these valve box extensions when your system is buried a little deeper. use the 6" valve box extension with a 12" deep box for a total depth of 18". these durable boxes and lids are made of high density polyethylene (hdpe) for strength and good chemical resistance. all dura valve box products carry a scte static vertical load rating of "light duty pedestrian" and are not rated for vehicle traffic.<br /></p><p>dura products are proudly made in the usa.</p>