Customs exemption for steel tubes used in gas cylinder manufacture, subject to compliance, recordkeeping and duty recovery on breach. The notification exempts imported steel tubes under Chapter 73 used to manufacture gas cylinders conforming to specified Indian Standards from Customs duty in excess of an amount calculated at a prescribed ad valorem rate, subject to an importer's undertaking requiring exclusive use for the manufacture, maintenance of prescribed consumption accounts, production of manufacturer-certified extracts within three months (or extended period) and payment, on demand, of the duty difference if the conditions are not met.