Hillman 1/4-in Bumper (25-Pack) Door Stop in the Door Stops department at Lowes.com
Black Rubber Stopper, #4 for 25mm Tubes
Dorman Rubber Stop Assortment 961-375D | O'Reilly Auto Parts
GSC Go Science Crazy Rubber Stopper, Size 7, 1 hole 5mm in diameter:Stoppers | Fisher Scientific
T Type Round Silicone Rubber Stopper end cap rubber tube plug with 3mm hole for 8mm hole 8 8.5 mm 8.5mm 5/16" 21/64" Diameter|Printer Parts| - AliExpress