It is a good practice to replace your sealing washer with every oil change. These 10 piece kits are made up of 5 Copper washers and 5 Aluminum washers. The manufacturer recently decided to make half of the kit Copper washers as that is the material of choice for many OEM manufactures. This gives you the opportunity to decide which you prefer, but either will work great at creating a leak-free seal between the case and the drain plug.