I don't know if it's a function of thickness, or if they've beaten these researchers to the punch, but black widow spiders spin by far the strongest thread I have ever encountered. There's never any doubt when I encounter a black widow web, and that's how I know to proceed with caution, when I'm working in my garage on the next Google haha.
They might be twining multiple threads (each themselves consisting of multiple strands) together to make an especially strong dragline or something. The giant riverine orb spider is on record as making the strongest thread, but that might be under certain conditions (like what comes out of the spinnerette (sp?), no weaving allowed) or the like.
