The tripod mount ring mount on the tripod, it helps you fix and balance your tele lens which is heavy or long lens hanging off the front of camera. It is made by metal. The tripod mount is 1/4UNC.
Inside Ring Diameter is 65mm 
Compatible with:
Tripod mount ring for Canon EF 70-200mm f/4 L IS USM Lens
Tripod mount ring for Canon EF 70-200mm f/4 L USM Lens