From the moment you attach it, the Ap-604 Replacement Foot for Canon 400mm f/2.8 Is (I and Ii), 600mm f/4.0 Is (I and Ii) lenses offers a seamless integration with your camera setup. This high-quality, durable replacement foot is designed to replace the factory foot on the rotation collar of your lens, serving as an Arca-Swiss style quick-release plate. There's no need for an additional quick-release plate, making this a versatile and reliable choice for photographers.The Ap-604 Replacement Foot not only enhances the handling of your lens on conventional tripod heads, such as ball heads, but also simplifies packing due to its low-profile design. Its sturdy construction adds stiffness over the factory tripod mounting foot connected to a lens plate, effectively reducing flex and vibration. This ensures your lens remains stable and secure, contributing to improved image quality.This replacement foot also creates a more ideal geometry for using your lens on the Wimberley Sidemount Head and Sidekick, allowing the lens to balance optimally. It's worth noting that the Ap-604 Replacement Foot is compatible with a variety of Canon lenses, making it a versatile addition to your photography equipment.Finally, the Wimberley lens plates are compatible with Arca-Swiss style quick-release clamps such as those made by Wimberley, Kirk Enterprises, Really Right Stuff, Arca-Swiss, Markins, and others. This compatibility further enhances the versatility of the Ap-604 Replacement Foot, making it a valuable asset for any photographer using Canon Eos Ef lenses..