DELL XR11/XR12 COMPATIBILITY: Sliding rail kit designed as an alternative to Dell ReadyRails for PowerEdge XR11 and XR12 servers 2POST AND 4POST MOUNTING: Fits 4Post racks with 17.5-30.5 (444.5-774.7 mm) depth and 2Post center mount racks with 3-6 (76.2-152.4 mm) depth UNIVERSAL RACK FIT: Supports square round and threaded holes; works with L C and ? upright rack shapes EASY MAINTENANCE ACCESS: Sliding rails provide smooth extension for hassle-free maintenance and equipment removal DURABLE DRY SLIDE DESIGN: Built to last longer than ball-bearing rails ensuring long-term reliable performance