What is the thread size and pitch on the blue head magnum .15, someone said 6mm but it is not. Maybe 5mm? I need a safty nut but need size first so I can order it.[&:]

It's 5mm, the same as the OS .15LA, so anything that says it will fit the OS LA will fit.

I'm not sure about the pitch, but I think it's 1mm.

At least some of the Magnum manual on the older XL was wrong, and said 6mm, when that engine is also the same as the others, 5mm

I'm pretty sure that it's 5mm. I have 4 of them for combat and if I recall correctly I had to use the OS .10 (not .15) spinner nut.

yep. 5mm

Yes, it is M5 with the standard pitch of 0.8mm. Very common size, the AP 09 and 15 have this too for instance.

(For M6 the standard pitch is 1mm as hinted at above)