Winter Rubber Plug with Valve for 1-1/2 Inch Pipe, with Blow Thru Stem Open stem plugs have an opening that passes through the center of the stem. This opening allows the induction of air or water pressure into the system you are testing. 1/8" pipe thread and 3/8" hose barb on top of the plugs make them versatile tools to set up for pressure testing, clearing blocked lines, or blowing out lines for winterizing.