MRK-4431 Rack Spaces: 44U Space Features: -14-guage steel tops and bottoms, 16-guage seamless steel sides and 11-guage thickness where the rail brackets are welded to the sides, each model is equipped with laser cut 1/8" thick internal braces made from structural steel.-Standard front and rear adjustable 11-guage, 10-32 threaded, wide rackrail with numbered rackspace increments to speed equipment mounting.-Standard solid rear doors are configurable and accept a number of options for thermal management.-Abundant lacing points throughout the interior facilitate cable management.-Rail brackets are pre-punched for built-in cable management.-Removable rear plates allow cable bundles to be easily passed over or under the MRK"s standard key-locking rear door.-UL Listed in the US and Canada.-Seismic certified (UBC 1997 & CBC 1998 Zone 4; IBC 2000, IBC 2003, ASCE 7 - 02, NFPA 5000 Seismic Use Group III) for protecting 1000 lbs. of essential equipment when used in conjunction with our MRK-Z4 brackets. Includes: -1/2", 3/4", 1", 1 1/2" electrical knockouts found on removable rear plates, top knockout plate additionally includes UHF/VHF antenna knockouts. Construction: -Fully welded construction provides a 2,500 lb. weight capacity. Color/Finish: -Finished in a durable black textured powder coat.-Configurable open top accents a number of options.