T Type Round Silicone Rubber Stopper end cap rubber tube plug with 3.75mm hole for 10mm 10 mm hole 10.6mm 25/64" 13/32" Diameter - AliExpress Computer & Office
Amazon.com: Floor Jack Rubber Plug for Filler Hole, 10mm (1pc) : Automotive
Floor Jack Rubber Plug for Filler Hole, 10mm (1 Piece) - Walmart.com