The kirk lp 55 quick release lens plate fits canons 600mm f4 is usm ii 400mm f28l is 600mm f4 is 800mm f56 is 500mm f4 is ii 200 400mm f4 and 400mm f28l is ii lenses replacing the existing foot it provides a secure quick release capability with arca style release systems including kirk arca swiss arca tech and wimberley