Permission for job work requires authorization, time-limited return and mandatory sample retention to ensure no substitution. Permission for job work under the 100% EOU Scheme is a time-limited authorization allowing goods to be sent for subcontracting and requiring their return within a short prescribed period, with provision for discretionary extension. A mandatory sample retention requirement obliges retention of samples of goods sent and received after job work in the Central Excise Range office for a minimum period to prevent substitution; gems and jewellery are excepted from sample drawal.