Abstract: A modular unit for a shelving system includes a pair of tube connectors each made up of half-sections together having an outer transverse dimension slightly less than the inner transverse dimension of a tube to be connected thereto, a threaded fastener threaded through an opening in one half-section and abutting the other half-section to force apart the two half-sections and thereby to firmly clamp them to a tube, and a tie rod joining a half-section of one of the tube connectors to a half-section of the other tube connector.