As a box code, 4138 is used for 6 post office box locations.
PO Boxes using 4138
| Suburb | Town | Province |
|---|---|---|
| Clare Est | Dormerton | KwaZulu-Natal |
| Clare Estate | Dormerton | KwaZulu-Natal |
| Chesterville | Mayville | KwaZulu-Natal |
| Chesterville Ext 2 | Mayville | KwaZulu-Natal |
| Chesterville Ext 3 | Mayville | KwaZulu-Natal |
| Ridgeview Gardens | Mayville | KwaZulu-Natal |