1)Locked by butterfly hole structure and cargo dead weight,layer bearing capacity than type(A). 2)Eassy assembly and disassembly;limitless connection to main auxiliary rack;enhanced rack robustness 3)Save investment;layer plates arbitrarily adjustable at 75mm steps;steel,wood and other layer plates can be used. 4)Rack consists of uprights,beams,layer plates,safety pins and plastic footings