Fits any 4Post rack - Square, round, threaded holes. - Mounting depth of 12 - 32" (304.8 - 812.8 mm). - Dell rail kit not required. - Supports L, C, Z and rack upright shapes Alternative to Dell R720 rail kit - High quality, dry slide rail kit Fits any 2Post rack - Center mounts in 2Post rack - Works with 3 - 6" (76.2 - 152.4 mm) uprights The Dell PowerEdge R520, R720,R730, R820 Dry Slide rails are an alternative solution for the Dell rail kit that is provided with the R510, R520, R530, R720,R720xd, R730, R820 and R7910 server. This rail kit is not a ball-bearing rail kit. Dell PowerEdge R720 Slide Rails are compatible with standard 19" EIA-310 server racks, and can work with either 2 post or 4 post models. The device is designed to fit in racks using either standard square, round or threaded holes, and feature an adjustable mounting depth between 3 - 32" (76.2 - 812.8 mm).