The Ready Rails static rail kit for 2U systems provides tool-less support for 4-post racks with square or unthreaded round mounting holes including all generations of Dell racks. It also supports tooled mounting in 4-post threaded racks & 2-post (Telco) racks for added versatility. Designed For Power Edge R320, R420, R620, R720; Power Vault DL4000, NX3300