Based on this topic, I decided to finally repair a graphite casting rod tip that snapped just ahead of the first guide a few years ago. Don't ask how it happened.
Using a drill gauge set, I found that the ID at the break was between .060 and .065. I had nothing suitable so, with the tip section and micrometer in hand, I hit the spring drawers at the hardware store. Conveniently they list the diameter of the wire on the lid so the mic wasn't needed.
Found a single .063" spring for $3 which I was ready to buy when the Fishwife found the music wire rack. Three piece bundle of .062 music wire 30" long was $2.29. Figuring that the spring would be useless once I cut the end off, and that it was more expensive, I put it back and got the music wire. Fishwife seemed to think it was a bad idea to have all that extra wire left over and that I should just buy the spring and throw away the coils, even though it cost more... go figure.
I epoxied a 1" piece of wire into the joint, one end at a time. Since the break was right at the end of the thread wrap, the joint isn't even noticeable. Haven't fished it yet but it certainly was the easiest rod repair I've done. And I've got 89" of wire left over to use for something else... hopefully not another rod break.