The 1-1/4″ x 1-1/4″ Square Bore Set Screw Coupling – Steel (Black Oxide) is a simple and economical rigid coupling designed to connect two square shafts for reliable torque transmission. Precision-machined from black oxide steel, it uses set screws that secure directly into the shaft surfaces, providing a cost-effective connection where frequent adjustment is not required. Available with or without keyways, these couplings can also use a second set of screws to significantly increase load capacity.