eVic control head and tube threading specs?

[Dgephri]

I have a source that can probably machine a nifty alteration to the eVic and 18650 tubes for me...but the best I have found on the threading is M21 .75 or .80 pitch. Has anybody in the Modding area here confirmed pitch and # of turns on these threads?

ALL help appreciated...I will show my little gadget after I confirm it working.