Do you mean the rubber pipe that connects to the tank or a metal part that goes under the wing to secure the cap? My cap is non-standard and has nothing underneath except a pipe, which being the right length prevents the cap from moving upwards. The pipe is standard across all Aces I think, it is 60mm bore which when I sought a replacement (about six years ago) was not available except in very short lengths for a Mk2 Cortina. I paid for a rubber manufacturer to make a mould and then bought the first tube out of it, so if you need a pipe it should now be available at a sensible price. Let me know if you want the contact details.