Abstract: A cantilever rack structure has at least two wide flange I-beams comprising upright standards connected to each other and with stabilizing base members at their lower ends, the flanges of these standards facing forwardly and rearwardly and with the web between the flanges extending from front to back. One or both flanges of the I-beams has a vertical row of holes therethrough at each side of the web, the rows of holes being close to but spaced laterally from the web. Load-supporting arm members comprise a plate adapted to fit against the flange of an I-beam and a forwardly-projecting rigid arm extending from the plate, each plate having at least two laterally-spaced holes therethrough so that one hole registers with a selected hole in each of the two vertical rows of holes through the I-beam flange, and bolts with removable nuts secure the arms to the uprights. Connecting brace members extend from the front flange at one end to the rear flange at the other.