A coupling unites two short segments of trench shield spreader tubing into a single spreader tube of desired length. The coupling comprises a cylindrical insert adapted to fit snugly within and to extend a short distance into the interiors of two spreader tube segments abutted end-to-end, the total length of which becomes the spreader. Each coupling includes transverse retainer pin holes which align with like holes through the abutted ends of the spreader tube segments to admit a retainer pin. The coupling may include stiffener and spacer straps disposed on either side of the retainer pin holes that extend substantially the length of the coupling.