Sold as a single washer. Stainless steel on one side, neoprene on the other to seal water out. Commonly used in kayak assembly with 1/4-20 truss head screws. 7/8 in. diameter. Center hole takes a ¼ inch diameter fastener. (Alternative part numbers 3730-0312 and 01.1315.0063) Sold as a single washer. 1/4-20-HDW