Open stem plugs use the same straight-sided rubber, large wing nuts and corrosion-free materials as closed plugs except they have an opening that passes through the center of the stem. This opening allows introduction of air or water pressure into the system you are testing. National pipe threaded tops on the open stem plugs make these versatile tools easy-to-set up for pressure testing, clearing blocked lines or blowing out lines for winterization. The plug top is a combination 1/8 in pipe thread and 3/8 in hose barb. When using with the Anderson water and air pressure testers (PT14 and PT16) a quick connect fitting will need to be added to the stem (CL18 or CPH18).