Hard plastic adjustable focus ring :  If you’re looking for a more professional solution, you might consider a follow focus system. These typically include a hard plastic follow focus knob or wheel that attaches to a rig, allowing for precise focus control. They are usually quite sturdy and compatible with various lens sizes.

Rigit and very sturdy:  universaly adjustable focus rings made of rigid materials. These rings can be stretched to fit different lens diameters and provide a textured surface for focus control. They are often used for manual focusing in photography and videography.

When searching for a hard plastic adjustable focus ring, be sure to check the compatibility with your specific lens or camera setup. Additionally, consider the ergonomics and ease of use for your intended application, as a comfortable and sturdy focus ring can significantly improve your shooting experience.