I've been using #2 silk bead thread for several years on a VPI TNT with flywheel. Instead of tying a knot, I switched to gluing the ends together. The glue I used is called Liquid stitch. I made a jig by putting two nails in a board, loop the thread over the nails and then wrap the tag ends around each other and secure it with clothespins. Then I apply glue (not much) to the area where the ends are looped together. Once it dries I cut the tag ends off with a razor blade. I made two belts of the exact same length and have been using them as a double run for about 6 months. There is a slight bump as the glue joint goes over the pulley, but over time the glue joint "rounds out" somewhat. One advantage over tying a knot is that you can set you length more exactly. It's much harder to tie a weaver's knot or double uni knot and hit an exact length.
