Fastback tank fuel taps

I bought a fastback tank over the weekend and it has larger threaded holes for the fuel taps than the 1/4" BSP threads I usually find on Nortons. Anyone have this experience and know what taps can be used?
The tank is from '69 to '72 as it doesn't have the recesses for the round badges. The threaded holes appear to be original.

stolen reducers

Hi Dave
The fastbacks and others had 3/8x1/4bsp reducers that are bonded in after manufacture of the glass work. They are available from mcmaster-carr and domiracer among others

you can see a pix here on my site
http://www.gis.net/~dynodave/ntfbrgls.htm

fuel tap thread adapter

Dave,

I found the adapter on the McMaster-Carr website, part number 4860K657. This is a nickel plated brass fitting. Is that what you use? Thanks a lot for the reference!

How are these bonded into the larger inserts that are molded into the resin? Obviously I don't want any leaks.

Thanks,

3/8 -1/4 adaptor

I bond them in with some epoxy painted on the joint at nip up time.
The mcmaster ones should function OK, but the last domiracer ones I got, were the wide brass ones....closer to OEM (a little closer to cometically stock).

Oh yeah I remembered, it's the 72 combat glass interstate tank that uses the same adaptors.

fuel tap thread size

Thanks again Dave for the information. I printed the adapter drawing from McMaster and am going to try a plumbing supply very close to my office today. I would not have expected british thread sizes at US supply companies.