The photos below show 50# test kite line with a very light tension bead for adjusting the line.


Eighty of these beads, weigh about 1 ounce. You can buy them, and line, at kitebuilder:
A bead plus 3 feet of line weigh about .7 grams. So you could add 6 such sets to a tarp for a total weight of about 4.2 grams or about 1/7 of an ounce total.
The bead is just big enough to operate with gloved hands. It is about 3/4″ long and thicker at the middle. This really helps when grasping it and moving it up or down the line. There is just enough friction to hold the bead in place, even when not under tension. So the line stays as it was last adjusted unless something pulls firmly on it.
They also sell a larger bead which uses line up to 100 lbs.

