Abstract: A closure device or "zipper" particularly suitable for use with heavy water-tight containers to provide the secure joinder of an opening formed in the container and which can be readily separated to provide access to the interior of the enclosure and/or to permit removal thereof from the object the container is covering. The closure is formed from first and second pieces which are fabricated from a resilient material such as a suitable plastic, each of these pieces having an attachment flap at one end thereof which is secured to an edge portion of the enclosure which is to be joined to an adjacent such edge portion. One of these pieces has an upstanding elongated fastener strip with alternate rib and groove portions which run laterally from the main body of the strip.