KO thread does not damage Swarovski crystals at all. But crystals can damage any kind of thread. I use crystals sparingly with any kind of thread in this manner: I always put a seed bead on each side of a crystal so that the thread bends at the smoother seed beads instead of the crystal.

If you are using crystals only, try using Fireline. You can get it at the bead store, but if you love it, you can get LARGE rolls of it at any fishing store. It is braided fishing line with a steel core, so it is less likely to be cut by the crystals.

Thanks for answering the question I meant to ask! I'm not sure what I was thinking when I phrased it the way I did.