remarkably intact single-sided antique american depression era "magnetorque" porcelain or vitreous enameled cold-rolled steel a. finkl & sons gantry or overhead crane sign designed and fabricated by the burdick sign company, chicago, ill. the large cold-rolled steel sign with white and cobalt blue porcelain enameled finish was originally mounted against the crane's overhead hoist walkway railing. magnetorque is known as a form of transmission based on the principle that a magnetic field of force is produced whose strength is varied so as to transmit a torque of corresponding magnitude. With a system of this kind, control of any particular operation is effected through the agency of the magnetorque clutch, while the motor runs continuously at constant speed. the p & h crane sign is intact, but needs further cleaning to remove the caked oil and grime that has accumulated over the decades. measures 48 x 14 1/2 inches.