Open plugs have a hollow center stem that allows for the introduction of air or water pressure into the system you are testing. These heavy-duty and versatile plugs feature straight-sided rubber, large wingnuts and corrosion free materials. National pipe threaded tops on the open stem plugs make them easy to set up for pressure testing, clearing blocked lines, or blowing out lines for winterization. The plug top is a combination of 1/8" pipe thread and 3/8" hose barb. When using Anderson Water & Air Pressure Testers (PT14 & PT16) a quick connect fitting will need to be added to the stem (CL18 or CPH18). Straight sided rubber is the best choice for accurate, safe pressure testing in swimming pool plumbing lines, but it’s important to choose the correct sized plug. We recommend choosing a plug size that is about 1/8” smaller than the inside diameter of the pipe opening you are plugging off. The measurement listed for each size is the actual diameter of the unexpanded rubber.