The top one you may have seen before, this is the surgical tube Self tensioning inserts i made for my rainfly.
The others are new cheap and easy model made with guy line, and a rangerband (ring of bicycle inner tube).
Take your guyline and put thru ring. (go about a third, half turned out a lil short on one end).
Tie a knot in the line.
stretch out band, keeping line taut,and hold,,,
Mark line with pen, while you are holding stretched band to….
Mark should be at the end of stretched band.
Tie knot around band, keeping the mark on the inside of the knot.
When done the mark is tight on the inside of the knot.
Tie your loops on each end, or not if you decide to tie to existing lines.
And Voila, you now have self tensioning guy lines for your tent or rainfly.