StarTech.com 2.4 x 3.9in Vertical Cable Management D Ring – 1.5U Metal D-Ring Hooks – Wire Organizer for 2 or 4-Post Network/Server Racks (CMHOOKMW) – Cable management ring – black – 1U – for P/N: RACK-18U-20-WALL-OA, RACK-21U-20-WALL-OA, RACK-24U-20-WALL