Dave,
I know that these are standard nozzles and not made specifically for Webasto burners so the treads should be the same as any other small oil burner nozzle in the size range of 1 gph. Not sure that helps you much but a call to Delavan or one of the other nozzle manufacturers should give you the info you need. They use a .35 GPH 60 degree in a B pattern I think for a nozzle in these units.
Later Ed