Spoke nipple size 6.0 or 6.2

6 mm has been on all the harley wheels I have done but they were older. Someone else may chime in if they have changed. I will tell you if you need spokes,nipples or tools Buchanans Spoke and Wheel out of Cali sell top notch stuff. I have used Jp cycle spokes and they were junk compared to Buchanans. Also if you order a set of spokes from them you can buy extra nipples and or an extra spoke or two this way if you run into trouble you have one on hand.
Before you try to tighten them put some penetrating oil on them overnight. If you get a size bigger and a size smaller wrench it is useful if they have heavy chrome or start to round off the hex.

I never used that tool. I took one of their wrenches and welded a 1/4” drive socket to it and I use it like a dog bone extension. Their wrenches are good. I can’t believe the price of them now but that is everything these days. I think i paid $8 or $9 each for them 25 or 30 years ago
But I found that going by feel and the sound they make when u tap them with the wrench a better way than the torque wrench.