Designed for Canon EF 70-300mm f/4-5.6L IS USM, make it convenient for you to adjust the lens after fixing on tripod. Ring inner diameter: 81.5mm, Ring width: 18mm, Ring thickness: 4.5 ~ 8mm, Color: White, soft inner. Made of strong & durable aluminum, fine workmanship ensure perfect conformity in color and surface qualities. Spin the knob, pull it out to unlock it, tightened locking system. With a 1/4\" female screw on the bottom. With a 1/4in female screw on the bottom.