Expansion tank thread

[hoofa]

Anyone know what the thread size is on the expansion tank with the blue cap ?

[QBee]

Not got a micrometer, but as far as I can tell with a tape measure, it is about 6 turns of the cap to 2cm height of the tank thread, so around 3mm pitch.

I noticed when I compared them that it looks to be the same pitch as the expansion tank cap on my Saab 9-5, which is common to a lot of other cars according to adverts on the Bay of the E.
Hope this helps in some way.