Small but tricky
Five 5×5 boards and three 6×6 ones, classic rules, 2 to 5 threads each. Small does not mean quick.
With so few threads on the board, each one has to wander: a single pair can fill half the cloth. That leaves lots of room for wrong turns, and forced moves run out early. The levels go up in difficulty, from the first 5×5 to the last 6×6.
Two ideas help most here. A thread with a long way to go usually hugs the border — see long threads. And since every level has exactly one solution, you can rule out moves that would allow two — see using the single solution.