Guess on proper spoke wrench size?
 

I'm visiting rels for the holidays, and have a beater mid-90s Trek 820 here that I'm fixing up. Many components have been changed on it; the wheels are not original. They are Araya rims w/Shimano hubs that look 1990s-ish and I've attached a photo closeup of one. The question: what size spoke wrench (black, green, red) should I buy for truing purposes? I don't have a caliper handy. Your guesses/suggestions are appreciated!

I can't tell which spoke nipple size these wheels have by looking at a picture.

If you have different spoke wrenches available, then use whichever one fits on easily but with the least play.
If you need to figure out which spoke wrench to order, I can't help you. If you want to buy one, go to a shop (probably on the 26th I guess) and bring the wheel with you so you can match the spoke wrench size to the spoke nipple size.
Or just get one of the handy spoke wrenches that includes all 3 sizes - that's what I use at home.

Red is far and away the most common for factory wheels.
Black is most commonly needed for hand built wheels that have DT or Wheelsmith spokes.
Green is sometimes found on European wheels but it's not common anymore.

For no more than spoke wrenches cost I'd get both a red and a black. Oftentimes on older bikes a nipple or two has been replaced and they're no longer all the same size. I don't like the ones with all 3 sizes because, if you have to do very much work with them, they hurt my tender little fingers.

Thanks, RG. I'll try red.

Along with shipping costs and all, or the LBS price cutting that down - buy all 3. You will find use for them yourself, or be able to sell/trade with someone down the road. They aren't that expensive. And those Park color-coded one's are the one's most people like the most. Very comfortable and accurate with their short-reach.

Red

Black.

Pedro's has a nice spoke wrench that has all three common sizes everyone has mentioned before and is very well made.
http://www.pedroscatalog.com/images/560/6460400.jpg

Park makes a tool similar to what the previous poster mentioned. I would recommend just going with one of these multi deals. Then regardless of what size you have it will work.

get them all or the three size one.

Nothing is more frustrating than not having the right spoke wrench.

+1
Basically those multi-tools suck. They're almost sure to round off the nipple shoulders sooner or later.
I recommend Spokey wrenches and would guess that the yellow spokey would work well for you. Spokey's don't slip. I don't like the earlier Park spoke wrenches but suspect that the newer "4-sided" types grip better.

Al

And the winner is: RED !
I should have spelled out that I already have all three colors of spoke wrenches at home, but don't have my tools with me. Thus, I didn't want to purchase too many duplicate tools while visiting. Based on the suggestions, I bought a red one, and that worked fine.