Hillman 2-Count 3/8-in Rubber Standard Flat Washer in the Flat Washers department at Lowes.com
Premium Quality EPDM Rubber Washers 7/8" OD X 1/4" ID X 1/8" Thickness 70 Duro
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6 Thick Neoprene Rubber Washers - Gorilla Gasket
Amazon.com: Black Rubber Washer Large Rubber Washers 1" OD x 3/8" ID x 1/8" Thickness - EPDM Rubber Washers Flat Rubber Washers Round Rubber Washers (Pack of 25) : Industrial & Scientific