A structure comprising a plurality of regular hexagonal tubes and a plurality of rhomboid inserts is disclosed. At least one of the tubes can be placed end-to-end relative to another of the tubes in a configuration where the central axes of the tubes are parallel. These central axes can be either collinear or not collinear depending upon the overall configuration of the structure chosen. Each rhomboid insert fits inside at least one section of a hexagonal tube. Those rhomboid inserts that fit into more than one hexagonal tube provide a means for interlocking the tubes.