A compression lock on a connector for a shelving post has upper and lower, mating collar parts having distal ends encircling more than 180 degrees of the post but separated by a gap through which the post can pass. Each distal end has an axially extending projection with a rounded end and a recess adjoining the projection. The projections of one collar part mate with the recesses of the other collar part to interlock the collar parts around a compression sleeve and form a frusto-conical inner surface that wedges the a mating sleeve against the post to affix a shelf attached to the connector.