The Canon Tripod Mount Ring B (B) is the tripod collar for the 100mm f/2.8L USM Macro EF 100mm f/2.8 Macro USM MP-E65mm f/2.8 EF 180mm f/3.5L Macro USM lenses. A reducer adapter is included. This mount ring is a part of the high quality and dependable Digital Camera Accessories from Canon. All of the features you need for a price you want. Digital Camera Accessories from Canon are well known for their quality and Canon Tripod Mount Ring B (B) for Macro Lenses upholds that standard.