I use MASTEX Upholstery Thread. This is pure nylon bonded and it is very strong. You can buy it at Intercal. Here is the link. Scroll down on the page to see the thread.
I use artificial sinew for thread jointing. I find that its stickiness allows for less slippage when tying my knots. The strands can be split into two or three strands. Artificial sinew is what taxidermists use for sewing and it can be found at Michael's, Tandy Leather and some of the bear making suppliers.
Artificial sinew is a waxed nylon thread. It is extremely strong so it is great for setting eyes or string jointing. It can also be used for sewing real fur and leather. Here is a good picture of it. http://www.bushcraftuk.com/forum/showthread.php?t=32973
It's the only type of thread I haven't managed to break.
I have managed to break it but still swear by it, I have and do use it for everything .Eyes, ladder stitching, sculpting, jointing. You name it I have probably used it for it. I honestly could'nt live without the stuff. I go through a large roll a year.