Found an old lecture at a thrift store. Thought it would be perfect as a puzzle center. But heavy and very difficult to move. Not to mention floor markings. These rollers looked pretty small for the job, but the specs were right. Solidly made, with high-quality materials, easy to attach to the leash, a locking function is needed, and they move the puzzle beast like a hummingbird in flight. Terribly pleased with me. I mean roles.