Ans. CNG cylinders are manufactured from a special steel alloy and are seamless in construction. Their compact size allows them to easily fit even in a small car. An empty CNG cylinder with a 50 litre-water-carrying capacity weighs 48 kg, with a length of 835 mm and a diameter of 316 mm. The 50 litre capacity cylinder is the one most regularly used; cylinders with 45 litre, 55 litre, 60 litre and 65 litre capacity are used as well.