A system and method are described for a variable mount arm assembly for installing support structures within different types of rack systems. Embodiments of the invention disclose a rack system support member comprising a rotatable bracket having first and second mounting interfaces on first and second mounting faces of the bracket. The rotatable bracket can be secured in a first position to mount the support member in a rack system that uses the first mounting interface. The bracket can be released from the first position and rotated to a second position to mount the support member in a rack system that employs the second mounting interface.