ADJUSTABLE DEPTH: Quickly adjust server rack installation depth ideal for racks that are too long or too short. UNIVERSAL COMPATIBILITY: Works with square threaded and round hole racks in 4-post configurations supporting most major manufacturers like Dell HP and IBM. DURABLE CONSTRUCTION: Rated at 50 lbs per rack unit offering strong support for up to 300 lbs in 6U configurations. HIGHLY CONFIGURABLE: Brackets can be combined to increase U height and allow more flexible equipment mounting. NOT DELL READY RAIL COMPATIBLE: The 1UBRK-059 model is not compatible with Dell Ready Rails.