These are specially made for Lambretta upgrades in the U.K. from top quality gasket material, with far superior sealing qualities. Specifically used for fuel and oil under pressure unlike standard gaskets.
They are standard thickness but the outer is cut to suit an A.F. and similar PHBH manifold, so it is bigger than standard inlet gasket, giving more surface area to seal.
The gasket material is made from aramid and man-made mineral fibres bonded with nitrile rubber. Suitable for sealing out oils and fuels, also water, steam, gases and many chemicals!
The inside hole will need to be cut to suit if you've had your inlet opened up as it is based on a standard, uncut inlet