what size tap for the heater fitting?

[blizz]

so i worked on it today and got most of it out. i now need to tap the threads so i need to know what size to get. anyone know?

 

[the 18th letter]

so i worked on it today and got most of it out. i now need to tap the threads so i need to know what size to get. anyone know?

At work now but I'll let you know when I get home. Did mine this spring. I would send u the tap BUT i don't plan on selling my yukkie and may need it again!! LOL