fibre washes used on gas pipes

[plumbdoctor]

I remember something about using certain fibre washes on gas pipes can someone refresh me because when installing a combi this week i lost a washer for the gas pipe where it connects to the boiler jig and im wondering if i can use a fibre washer the same size from my spares pack ?

 

[Billy Bob Bob]

some manufacturers use boggo green ones some use blue some use rubber if its a fibre washer you have lost i would have no issue using a standard green type