NORMAN NIPPY MK5, AND MANY OTHER BRITISH MOPEDS AND LIGHTWEIGHT MOTORCYCLES NO NEED FOR A SEALING WASHER ON THE TAP MAIN THREAD AS IVE NEVER KNOWN ONE TO LEAK WHEN SCREWED INTO THE PETROL TANK THREAD BUT IF YOUR EXTRA CAUTIOUS JUST WRAP A THIN AMOUNT OF PTFE THREAD TAPE AROUND THE THREAD BEFORE FITTING.