New Hejnar Photo Quick Release low profile foot replacement for:
Canon EF 400mm f4.0 DO IS II
To remove the Canon foot, use the M3 hex key tool that comes with the H133 to completely remove the four Canon mounting screws.
To install the H133, use the four provided with H133 screws and secure foot to the lens collar.
If your mounting screws loosen over time, consider using of LocTite 242 for security.