No. 6 Rubber Plug for 1 Inch Fitting Safely seal off in-ground plumbing lines during freezing conditions! Winter freeze plugs are used to plug your swimming pool pipes after they have been drained to prevent water from entering the pipes and causing freeze damage. The rubber expansion plugs are non-corrosive construction made of heavy-duty nylon, stainless steel, and high quality rubber. Simply screw plugs into all return and drain inlets after blowing out lines. Features stainless steel bolts and washers and large plastic wing-nuts.