These are 10 copper washers with a 2 mm thickness, designed as solid gaskets and oil seals for sump plugs in boats. The set provides a range of sizes to fit common bolt diameters from M3 to M21 mm, offering reliable sealing across multiple marine applications. The product title includes a dimension reference of 6x17.5x2 mm, reflecting the listed size format. Key benefits Effective sealing: copper crush washers deform to fill gaps, creating a tight seal for sump plugs and other fittings. Corrosion resistance: copper provides durable resistance in marine environments. Versatile sizing: includes multiple inner diameters (M3, M4, M5, M6, M7, M8, M10, M12, M13, M14, M15, M16, M17, M18, M20, M21 mm) to fit a wide range of bolt sizes. Ready to use: solid gasket design for reliable oil sealing in boats and compatible equipment. Key attributes Quantity: 10 pieces Material: Copper Thickness: 2 mm Sizes included: M3, M4, M5, M6, M7, M8, M10, M12, M13, M14, M15, M16, M17, M18, M20, M21 mm Dimension reference noted in title: 6x17.5x2 mm Application: Sump plug oil seal and general copper washer sealing for boat and related fittings Specifications and compatibility Function: Solid gasket and oil seal for sump plugs and other bolt assemblies requiring copper washers Compatibility: Designed to fit standard bolt sizes from M3 to M21 mm as listed Material performance: Copper provides malleability for effective sealing and good resistance to corrosion in marine environments Dimensional note: 6x17.5x2 mm dimension is included in the product title reference Use cases Boat engine sump plug sealing: worn or damaged washers to prevent oil leaks Marine fittings and drain plugs: seal connections where copper washers are specified for a tight, leak fit General mechanical sealing: suitable for bolt assemblies in compatible hydraulic or piping connections requiring copper washers Installation guidance Inspect surfaces for cleanliness and remove old material before installation Place the appropriate size washer between the bolt head and mounting surface Tighten to the specified torque for the bolt size and material; avoid overtightening to prevent deformation washers if they show signs of deformation or wear to maintain seal integrity Care and storage Store in a dry, cool place to prevent oxidation beyond normal patina Handle with care to avoid bending or crushing the washer before use This description stays aligned with the product's brand, specifications, model, and features, providing clear, customerfriendly information to support informed decisions.