Rubber expansion plugs with a nylon wing nut allow you to quickly plug your plumbing lines to keep water out during winter. Known as expansion plugs, freeze plugs, rubber plugs, hole plugs, pipe plugs or just pool plugs, you can use these expandable rubber plugs for pool returns, cleaner lines and skimmers to prevent the pipes from filling with water and freezing during winter. This plug is designed for 3/4-Inch smooth pipe. Plug # 3