Concessional duty on leased machinery applies where temporary imports are re-exported after use under bond and timed conditions. Concessional customs treatment applies to leased machinery, equipment or tools temporarily imported for contract execution where the importer declares temporary import, re-exports within three months or an authorised extension up to eighteen months, and furnishes a bond with bank guarantee; extensions require payment of duty difference and delayed re-export attracts additional duty calculated by graduated notional rates, and such imports are not eligible for drawback.