500ml ideal squeezing action double chamber liquid fuel-dispensing bottle for a multiday trip | luzernpackaging Twin neck bottles are containers with two bottles and two necks, the necks are usually the same size.Just fill the main chamber with fuel, flip open the measuring chamber cap, then squeeze the bottle to fill the measuring chamber to the desired level, now pour the measured fuel directly into your stove. No need for a separate measuring cup, measurement is built right into the bottle. The squeezing action moves the fuel from the main chamber up the side tube into the measuring chamber.They're often used for fuel additives, fertilizers, or products that need diluting.They're made of HDPE plastic, through fluorination treatment to enhance chemical resistance and come in a variety of capacities, sizes and shapes.