Extreme Max Universal Cup Holder is designed for easy mounting on rails, posts, pipes and posts from 5/8" to 1-1/2" thick. Its universal design allows compatibility with a variety of beverage containers, water bottles, wine glasses, beverage cans, drinking glasses, glass bottles, sippy cups. . . The open side even holds cups and thermos handles, making it the perfect holder for any drink. The cup holder mounts quickly and without any tools; a simple worm clamp with easy to use thumbscrew fixes the cup holder securely in the desired place. The rotating bracket design keeps your cup holder vertically, regardless of its mounting position or external movement. The durable and lightweight aluminum construction provides excellent protection against rust and other damage.