fibreglass fuel tank

i have just bought a 1970 commando and it has a fibreglass tank.Was this a genuine thing or an aftermarket part ?any help would be appreciated .

It is probably genuine, a pic would confirm. In 72ish fibre glass tanks were outlawed on new UK bikes so they switched to steel. You will need to get it sealed as the ethanol in todays petrol eats that type of tank and causes leaks and sticky deposits in the carb and on the inlet valves etc. Or change to a steel or alloy tank if they are available for your model.

fibreglass is correct unless you hace a fasback long range, steel roadster and interstate did not come available to 1972

Thanks for your help.