DSLRKIT Tripod Collar Mount Ring C (WII) for Canon 70-300mm f/4-5.6L The third party special design, perfect conformity in color and surface qualities. Ring inner diameter: 81.5mm, Ring width: 18mm, Ring thickness: 4.5-8mm, Color: White Made by metal with very high quality Suitable for Canon EF 70-300mm f/4-5.6L IS USM. The UNC (Unified National Coarse Thread) is 1/4" and 3/8".