Beautifully engineered locking fuel cap and adapter. Manufactured to the highest standards and built to last a lifetime. Fits all 2” male or female tanks. Cap and adapter are made from high quality carbon steel, CNC machined for precise fit and function, case hardened for durability and resistance to drilling and damage. Once hardened the cap and adapters are silver zinc plated for corrosion resistance.resistace. The cap has 4 elongated slots machined on the shoulder to allow for a certain fit of the padlock (not included) with either one of the 12 5/16th's holes provided in the adapter. The cap has been machined with 8 finger grooves to allow for a firm grip of the cap when tightening on to the adapter.There is a 10” stainless steel retaining chain attached to the inside of the cap to retain the cap to the tank during a fill up. The adapter inside diameter has been increased to allow for large fuel filler nozzles to fit for fast filling at truck stops. A gasket has been precisely fitted inside the cap to prevent vapor or fuel leakage. THIS CAP IS SEALED AND TO BE USED ONLY ON A FUEL TANK THAT HAS INDEPENDENT VENTING