Where fuel is filled: gas caps

Fuel caps to screw or twist on or to flip open should be leakproof. Fuel caps prevent dirt from entering the tank unintentionally. They also prevent the contents from spilling over. And until the introduction of a separate tank vent due to increased environmental protection requirements, the vent for the tank was usually also located in the fuel cap.

Screw-on fuel caps

Stock with 1.5“ fine thread until 1936 or with 1.75” thread with 4 TPI pitch from 1982. Many custom gas caps with a different mounting use the 1.75” thread for adapter parts, e.g. ‘Monza’ flip-top caps or the high-end gas caps from Tolle. Fine-pitch threads for customizing are available from Dock66.

Bayonet-type gas caps

Stock type from 1936 to 1982. Since bayonet studs of different heights were used and it is also not always clear whether an original gas tank or an accessory gas tank is mounted on the Harley, sometimes the only way to find out is to try it out.

Swing-open gas caps

Can be found in the accessories and customizing sections, for example on the racing-inspired “Monza” gas caps.