Rubber O Rings Kit Assortment 10Pc × Clear/Black Conical Rubber Stopper Blanking Plugs Silicone Tapered Plug Seal End Cover Caps 1.5-16mm for Oil or Air Sealing, Professional Plumbing (Size : 1x6x3: Amazon.com:
Hillman 0.5625-in Black Polychloroprene Hole Plug in the Hole Plugs department at Lowes.com