Job work challan requirements govern transfers to job workers and trigger tax liability if goods are not returned. Inputs, semi-finished goods and capital goods sent to a job worker must be accompanied by a challan issued by the principal or the job worker effecting transfer, with endorsements by successive job workers indicating quantity and description. Details of such challans must be furnished in Form GST ITC-04 for the specified period by the due date (subject to Commissioner's extension). Goods not returned within the stipulated time are deemed supplied by the principal on the date sent, requiring declaration in the return and payment of tax with interest.