By basic 3 stage type being added the same width x depth additional shelves, the stage count can be increased. For examples : M5K1545123 (3 stage type single model)+M3TA1545CK (additional shelves)1 se t= 4 stage M5K1545123 (3 stage type single model)+M3TA1545CK (additional shelves)2 sets = 5 stage type