The gas spout is constructed with 2 parallel tubes, a large one from where the liquid comes out and a little one (which it the "venting") under the larger tube. The small vent tube allows air flow so a vacuum isn't created in the canister - this allows the liquid to flow.Come with yellow and black base caps, compatible with RotopaX fuel 2 gal Fuelpax 3.5 gallon Scepter may other gas water crude oil plastic cans 1 2 5 gallon, if only use the spout may fit for old gas can when use your old screw base cap.Made from superior plastic, bendable and durable, easy pour spout includes a vent so that fuel flows out easily and evenly.Yellow Vent Caps with RETAINING LIP to prevent from popping out of your can. Easy to install,drill required.Start with an empty can, Drill 1/2 inch hole at the back of your plastic can above the fill line, insert vent cap andit in gently with a rubber mallet.We suggest you drill a smaller hole to start with and work your way up to the 1/2 inch drill bit. Be sure to drill a straight clean hole don't swagger side to side with the bit so you won't make a bigger hole than you need.Specifications:Screw Collar Caps Type: Fine ThreadSize(Long):approx 9 inch Long with Gasket is approx1-1/2 inch WideColour:yellowMaterial:plasticPackage Contents:3 * Fuel Can Spouts3 * Coarse Screw Collor cap3 * Spout Stopper Caps3 * Vent CapOnly the above package content, other products are not included.Note: Light and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.