A universal joint allows two TECHNIC axles to join at an angle. While useful for transferring motion, they cause fluctuations in the rotational speed of the driven axle which become more significant as the angle of the two axles increases.
LEGO have produced three universal joint parts:
|Part:9244a (Bricklink ID)||1972 - 1974||The first LEGO universal joint, it predated the TECHNIC line.|
|Part:9244||1977 - 2008||Introduced in 1977 with TECHNIC / Expert Builder.|
|Part:61903||2008 - present||Reduced in length from 4 to 3 units, making it easier to integrate in studless models.|
Set 970023 Universal Joints is made up entirely of universal joints.