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He proposed an improved design in 1936. Rzeppa"s design uses six balls and an inner and outer race to provide almost constant velocity torque transfer regardless of the joint angle. The joint works in a similar manner to a bevel gear with the balls bisecting the joint angle and functioning as the "teeth" to transmit torque.
The description of the two versions of the Rzeppa joint can be found in the United States patents 2,010,899 and 2,046,584.