They are a stimulating pleasure toy for one's anus. It looks like a thick string of pearls, with beads usually lined smallest to largest depending on the penetration preference. Can be used by oneself or with a partner(s). (Watch Made of Honor for visual reference)
As the horny lady sits alone she decides to stick the thunder beads in her butt to seek the pleasure she is yearning. The thunderbeads serve as a replacement for the erection in her anus that she yearned for. As the first bead entered the butt hole she yelped with pleasure. Slowly one by one the beads journeyed into the sensitive insides of her anus. She did not need a man to fulfill her needs she had her beads instead!