A bicycle water bottle cage holder is designed to securely mount a water bottle to a bicycle frame. Key specifications include material, size, and mounting method. Common materials are aluminum, carbon fiber, and plastic. Sizes vary, but many fit standard 21-26 ounce cycling water bottles. Mounting often involves screws attaching to dedicated frame bosses, or clamps for handlebars or other tubing. 
Key Specifications:
Material: Aluminum, carbon fiber, plastic, or a combination. 
Size: Fits standard bicycle water bottles (typically 21-26 ounces). 
Mounting: Typically screws into frame bosses, but some models use clamps for handlebars or other tubing. 
Weight: Varies depending on material (e.g., carbon fiber cages are very lightweight). 
Adjustability: Some cages offer adjustable features for different bottle sizes or mounting locations. 
Durability: Should be able to withstand vibrations and impacts during riding. 
Ease of Installation: Should be easy to attach to the bike frame with minimal tools. 
Compatibility: Should fit standard bottle sizes and mounting points on most bicycles. 
Additional Considerations:
Bottle Retention: The cage should securely hold the bottle to prevent it from falling out during riding. 
Accessibility: Should be easy to access and remove the bottle while riding. 
Aesthetics: Many cyclists consider the look and style of the cage when choosing one. 
Price: Prices vary depending on materials and features.