Sure - there are threads that could support a person's weight. The main question is, how thick does the thread need to be?

Also, threads usually have lots of strands in them, which is a good way to make them strong. I counted about 75 tiny strands in one piece of thread I have. I like the picture of spiderman's silk that I attached, because it shows strong silk that is made of many strands.

Here's one answer to the question: How thick a thread do you need to support someone's weight?

Kevlar is a strong material that is used for bullet-proof vests. It's about as strong as spider silk. Kevlar can hold 520,000 pounds per square inch. So if a kid weighed 52 pounds, a Kevlar thread would need to have an area of only 1/10,000 square inch over its cross section to hold the kid up, because 52 pounds divided by 520,000 pounds/square inch = 1/10,000 square inch. [I'd want a bigger thread than that, though, if I wanted to be sure that the thread wouldn't break; because maybe the thread wasn't perfect, and then it might break.]

So 1/10,000 square inch = 0.0001 square inch, and that's the area of the cross-section of the thread. I'm assuming the cross-section is a circle, and the thread is shaped like a long cylinder. That means the thread has a diameter of 1/100 square inch, or about 1/4 millimeter. [You can calculate that from knowing that the area of a circle = Pi times the radius times the radius. And the diameter of the circle is 2 times the radius.] 1/4 millimeter is not much bigger than the dot at the end of this sentence. Spider silk is a lot thinner than that, because it only needs to hold spiders and insects.

That would depend on how thin you would define a "thread", but nylon ropes a half a centimeter and less in diameter are easily capable of supporting a human, and ropes made out of protein (e.g. actual spider silk) would be thinner still.

I am familiar with various kinds of "threads" that can support human weight more from a practical than a scientific angle. In rock climbing, you use different kinds of "threads" to support your weight and more. First off, one important thing to understand is that a thread just enough to hold your weight would not work, because the force on the thread can be many times your weight if you swing on it, bounce on it, or fall on it when it is not taut. So while a single thin strand of steel wire, or a thin cord or nylon or (even thinner, because the material is stronger, Kevlar) can support human weight, items actually used for that purpose feature much thicker "threads". Ropes that can hold any kind of climbing fall (provided there are no cutting edges involved) are about the width of your pinky, and items attached to the wall to hold your weight or a fall might feature steel cables maybe an eigth of an inch thick. Nylon and to a lesser extent Kevlar "threads" are very susceptible to cutting while under load, so that is one thing where they might differ significantly from what Spiderman can draw on. The real big difference though might be the bulk that comes with a "real-world thread". While Spiderman seems to be able to generate more or less unlimited lengths of strong thread out of nothing (i.e. his body, like a spider), he'd be carrying quite a heavy load if he wanted to have a substantial length of real-world, weight-bearing thread with him all the time. I would estimate the bulk and weight of 200 feet of rope for climbing to be about the same as a gallon and a half of water.