Omar,

The large orange o-ring goes inside the cap and sits as deep in the cap as possible, in the inside corners. It's purpose is to seal the cap to the jug. The other orange o-ring goes on the fuel tip in the groove. It's purpose is to seal the fuel tip when inserted in the fuel cap. The black o-ring also goes on the fuel tip. It sits in the large groove at the top. It's just for grabbing the fuel tip. The white washers go between the cap & the 10-32 fuel fittings (fuel nipples that you attach the fuel tubing to). I'm not sure why there's 4 washers as it appears you only need 2. If you need further help you might drop slimline a note or call them directly. www.slimlineproducts.com email: [email protected]

Hope this helps.

David B