The HP Z640/Z840/Z8 G4 Rail Rack Kit (2FZ77AA) features enterprise-class, three-section ball-bearing extension rails. These rails are fully extendable, allowing the unit to slide completely out of the rack for servicing. Whether it is adding memory, swapping hard disk drives or installing an option card, upgrading a rack mounted Workstation is a snap. The HP Z640/Z840/Z8 G4 Rail Rack Kit rails installs into racks without using tools, making setup convenient and efficient. The inner slide and mounting flanges attach to the computer chassis using a set of screws for added strength and stability. The top mounting holes are concealed underneath the top plastic trim, which must be removed to attach the inner slide and mounting flanges.