Custom Lens Plate: Canon EF 400 mm.f/5.6 and other "A" Series II Collars CP-456 Mid length plate for various Type II "A" collar lenses. An ARCA compatible foot for the few Canon lenses using the "A" collar including: EF 400mm. f/5.6L USM It has a double cut dovetail to accommodate flash arms using the ARCA style mount. Securely mounts to the lens with our superior internal rib system for assured anti-rotation. Wrench, mounting, and anti-drop screws provided. Length 3.6" Weight: 1.6 ozs. Please be sure your Lens collar says " Ring A II (W or B) " As this plate will not fit older "A" style collars.