The invention is a connector for square tubing used in a system of construction and includes many designs but all having a plurality of orthogonal arms connected at a common point and including a wedge block at the end distal from the common point. The arm and wedge block have complementary sloping surfaces that expand the wedge block as it is moved up the slope by a draw bolt which enters the side wall of the arm, crosses the primary longitudinal axis of the arm and exits proximate the opposed wall where it engages the wedge block. The expanded wedge block secures tubing in place over the arm to the arm. The hex head draw bolt is recessed in the arm of the connector.