A shelving unit comprises a plurality of upright support posts and shelves having multiple corners with multi-component corner structure at each corner of the shelf for releasably connecting the shelf to the posts. Each corner structure comprises a two piece base segment and a substantially frictionless outside interlocking segment. The two piece base segment includes a housing fixedly connected to a shelf corner and a substantially frictionless inner liner within the housing. The outside interconnecting segment includes outwardly extending flanges that engage vertically oriented opposed undercut slots on the inner liner to facilitate interconnection of the base and interlocking segments. Both segments include partial frusto conical surface portions that engage a frusto conical clamping sleeve on the support posts to facilitate releasable connection of the shelf to the posts. The substantially frictionless material of the inner liner and outside interlocking segment enables ease of assembly and disassembly as well as a tight wedging fit of the components.