This image found on the web does not give the centerpoint for the barrel nut. I presume it's equidistant from each end of the fin head, but the drawing implies a difference inbetween each 70mm measurements. Can anyone confirm? I can't see a specified height above the baseline either. Does anyone know? Are there any better specifications/drawings for powerbox heads out there? I want to make heads and boxes and want to start with the best specs possible.
There are varying versions of power box's around.
I'd suggest using an Mfc fin base as a mold and go from there.-
or email chinook for a cad drawing
Barrel nut is centered.
Depth of the barrel nut (ie how long screw needs to be) can vary a tiny bit but think of it this way - you want it as close to the board bottom as possible, so there is more fin base holding it in.
And too far away from the board bottom = the nut thickness will interfere with the base seating in the box.
You will see the barrel nut is recessed into the fin (ie: sits below the sides of the fin base) by at least 0.5mm each side to allow clearance. So just measure the thickness of the base, the thickness of the barrel nuts, and position nut hole accordingly.
Somewhere on email I have the proper engineering dwg from Select Fins and searching is annoying me.... I hate tech
That's a pretty solid diagram and it implies the nut is centred.
Try finding a tuttle wave fin or two, you'll appreciate PB 
I've yet to find find 2 power boxes the same so whatever diagram you use to make one it probably won't fit all boxes
