Concessional duty on leased machinery: reduced duty on re-export based on duration, subject to declaration, bond and identification. Concessional duty applies to leased machinery, equipment or tools imported temporarily for contract execution, subject to a declaration at import, a bond with bank guarantee to re-export and present goods for identification, and re-export within prescribed initial or extended periods with payment of duty differential where extensions are granted; interest under section 28AB applies to unpaid duty and goods under this concession are ineligible for drawback under section 74(2).