Here are my basic re-rooting tools. A "hank" of synthetic hair, a needle that has had the tip of its eye snipped off, and a doll's naked head.
(okay......I'd been working on her already, so it isn't exactly naked)
The modified needle is probably the most wonderful tool idea for this purpose ever! This idea came from an article I have linked in my sidebar. I tried re-rooting with a needle and thread, but I couldn't find a needle long enough with an eye big enough that was slim enough to fit through the already existing hair holes.
So I took a regular sized needle with a large eye and snipped the very tip off with wire cutters. Be careful doing this because you don't want the tiny piece of metal to fly off into YOUR eye! It's also wise to wrap the sharp end of the needle with masking tape, like I did.
You will end up with this tool that looks like a tiny tuning fork!
Next, you'll need to wrap some strands of new hair over your finger quite tightly, then slip the tiny fork over them, so that they're caught between the prongs.
I apologize for the poor quality of these images....but I had to take the photos myself while doing this.
When you have the strands firmly held between the prongs,(use your fingers to keep tension on them) stick the little fork right into one of the old doll-hair holes.
Push it in, then pull it out. Voila! The hairs will stay inside the head! (This is for OOAK dolls that won't be played with by children by the way)
This is as far as I have gotten today. Stay tuned for more!