0.5mm diameter Gossamer Floss™ cord. Shimmery five-ply, squarish cord on 100-meter spools. Very strong, extra-stretchy, knots well. Double the cord for extra strength and add drop of Hypo Cement to knots for extra hold. Use with Igolochkoy needle/threader (#65-054) or size 10 (or larger) English beading needles. Do not crimp. Great for stretchy bracelets.
Gossamer floss is the best for beading with large hole beads - like 4mm cubes. It's strong and retains its shape. It will shred if the bead hole is small or if the bead edges are rough. Otherwise it's the best stuff.