This is the tripod mount for the Tamron 100-400mm F/4.5-6.3 Di VC USD telephoto lens, model A035. It allows for vertical and horizontal rotation, is easy to remove, and is Arca-Swiss compatible. I bought it thinking I might use it with a tripod, but time passed without ever using it. I even removed it when carrying the lens, and it's never been taken outside. I kept it thinking I might use it someday, but I don't think I will in the future, so I'd like to sell it.