Whilst you can buy pre-made heat shrink tee's, my general experience is that they are expensive and can be hard to find in small sizes.
I’ve used this method several times for most sizes of tubing and the only equipment required is:
- Standard heat shrink tubing,
- A heat source capable of shrinking said heat shrink tubing without melting it, like a hair drier, heat gun or even a cigarette lighter (please be careful with hot things, they can be burney).
- A craft knife, scalpel, exacto (I believe that’s what the Americans out there call it) or razor blade (please be careful with sharp things, they can be cuttey or stabby).
Step 1: Get Everything Together
I can’t stress enough how important it is to check you have all your equipment in one place and ready to go, there is nothing more annoying than noticing that you have forgotten to add a piece of heat shrink to a just soldered wire.
Start with two pieces of heat shrink tubing, the length is up to you really, but I find about 10 - 15mm or 1/2" is plenty, at the same time cut a piece around twice the length.
The longer piece is to become the branch of the tee, but does require some surgery to achieve its full potential.
You should just be able to make out the basic principal from the slightly fuzzy second pic, use your cutting implement of choice cut the longer piece of tubing along its length (down the middle) to about half way, then remove one of the halves being careful not to cut all the way through.
Then slightly taper the cut half towards the end, this makes life easier in a few steps time.