Replaces the factory foot of your lens, lowering the center of gravity for optimal balance Adds a built in double dovetail for Arca Swiss compatibility For Canon 100-300 RF F2.8, 400 F2.8 IS III, 400 RF F2.8, 800 RF F5.6 Anodized 6061 Aluminum, stainless steel fasteners Made in USA. Assembled in Charlottesville, Virginia About the AP-601 Replacement Lens Foot: The AP-601 replaces the stock foot on the Canon 400 f/2.8 IS III. 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 our lens plates. For use on the following Lenses: Canon 100-300 RF f/2.8 IS Canon 400 f/2.8 IS version III Canon 400 RF f/2.8 IS Canon 800 RF f/5.6 IS What's Included: AP-601 Arca-Swiss Style replacement lens foot (Qty 1) Mounting Screws – M4 x 14mm Socket Head Cap Screw (Qty 4) Safety Stop Screws - M3 x 6mm Socket Head Cap Screw (Qty 2) Hex Key – 3mm T-handle (Qty 1)Hex Key – 2.5mm (Qty 1) 10 Year Warranty on all products from Wimberley About Wimberley Replacement Feet: We use finite element analysis validated by empirical data when we design our feet. This process allows us to optimize the weight to stiffness ratio. Other manufacturers often reduce weight by removing material in ways that are convenient for the machining process or aesthetic design while ignoring stiffness performance resulting in rigidity below our quality standards.Not compatible with most Manfrotto or Gitzo clamps