While a simple tri-string can be made with just two sticks and a piece of string tied in a loop, there are many different elaborations on this basic design. This page provides a gallery of tri-string wands that may give you some ideas for making your own.
Homemade DipStix-style wand. Click here to learn how to make this wand from chopsticks and t-shirt material.
One of Thommy's early wands. Click on photo to go to Thommy's article.
Another of Thommy's wands.
Business end of one of Edward's favorite wands (circa 2011).
Another Thommy wand.
Business end of Todd K's wand circa 2010 (?)
Bamboo poles with dowel plug for tip (Rick Findley)
Homemade velcro straps to keep strings from tangling when not in use (Rick Findley)
Telescopic poles that extend to 54" (Rick Findley)
I use a small masking tape tab to mark the size of the top string in inches and also use a no. 2 or 3 1" swivel at the center of my bottom (sling) string. (Rick Findley)
telescopic pole with loop inserted an inch inside hollow tip with a drop of superglue inside. I also use zip (wire) ties as pictured. (Rick Findley)
I use a simple 'thumb knot loop' (the proper name for this is a marlinspike hitch) which you can either tighten onto the end of your stick or pull tight to make a loop and then hook into the carabiner or whatever you are using on the end of your stick. I personally favour a simple clothes peg.