Standard caps often don't hold up for long facing you with the need to replace them. All of our stainless caps carry a lifetime warranty. See our Solid-Pack Measuring Tips. Air-Cooled Insulated Caps have larger 15 5/8" outside flange diameters which allow them to fit on double wall and triple wall air insulated pipe. The internal venting allows for cooling of the pipe while keeping the rain and animals out. See our Air-Insulated Measuring Tips