Tax Deduction at Source: one percent withholding on specified supplies with prescribed remittance, credit, and refund rules. Section 51 mandates specified public and notified persons to deduct tax at one percent from payments to suppliers where contract value exceeds the threshold, excluding listed taxes from the value, and exempts deduction when supplier location and place of supply differ from the recipient's State or Union territory of registration. Deducted amounts must be paid within ten days after the month of deduction; a prescribed certificate of deduction is required. Deductees claim credit in their electronic cash ledger from the deductor's return under section 39(3). Nonpayment attracts interest under section 50(1); defaults are determined under sections 73, 74 or 74A, and refunds follow section 54 subject to a proviso on ledger credit.