Sorry, I should read more carefully - I thought that you meant the female thread for the canti retaining bolt
I've seen removable posts with both M6x1 and M8x1.25 male threads. I don't think that there is a standard for these - Magura and Marzocchi are both M6, or at least the forks I have are.
I've got a couple of M6 threaded ones if they're any use to you ?