This Wimberley AP-601 Replacement Foot suits the For Canon: 400 f/2.8 IS III / 400 RF f/2.8 IS
The AP-601 is precision machined to slide right into an Arca-Swiss style quick-release clamp.
It also has 1/4" and 3/8" tapped holes for mounting to non-quick-release tripod heads and monopods.
All replacement feet feature the same dual safety stops and flash bracket compatibility as the lens plates.