The Postcode Unit is the second part of the Inward Code. It is the 2 characters added after the postcode sector. Each postcode unit generally represents a street, part of a street, a single address, a group of properties, a single property, a sub-section of the property, an individual organisation. The level of discrimination is often based on the amount of mail received by the premises or business. In the postcode DH6 4SB , SB is the Postcode Unit.