Didn't you mention you have/or had a Husqvarna?

4.5mm nipples

http://husqmotoparts.com.au/find/part/M.4668

 

#9 Thread Size does NOT equal #9 gauge...2 different things

Measure the OD of your thread

"googoo" is your friend
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I do but it is still in Oregon.

 

See Post # 22... You stepped on it

 

On the table you linked to, "10ga, 9ga, 8ga" etc are listed in the thread size column. Are those different then a 10x32, 8x32, etc thread size of normal bolts?

The "OD" of the threads of the spoke are 4.30mm/0.170"

 

I was getting to it.

 

Threads of the spoke next to a caliper opened to .500"
It looks to me to be 16 threads in the 1/2". That would be 32 tpi.
32 tpi would be 0.79375mm thread pitch. Pretty darn close.

 

9 ga = .114"
8 ga = .128/.129"

#10 thread = .190"
#9 thread = .177" (if there was such a thing)
#8 thread = .164"
4.5mm = .177"

 

The major diameter of the spoke threads is 0.170".
The minor diameter of the spoke threads is about 0.155".
So the actual diameter is somewhere between.
Definitely not 4.5mm/.177".
The #8 thread at .164" sounds good but the 8x32 tap fits loosely in the nipple and the die won't go on the spoke at all.
I don't know where I got it but I have written down that #8 is 5/32" or .15625". Where did you get .164"?