Universal joints and universal shafts are versatile components for transferring rotary motion and transmitting torque from the driving to the driven unit. If two shafts set at a certain angle are connected using a single universal joint and one shaft turns with constant velocity, the other shaft will move irregularly. 

This non-uniformity – also called gimbal error – means that angle of rotation of the second shaft slightly lags behind or leads the movement off the first shaft, with kind of sinus-shaped variations. The greater the operating angle, the greater the non-uniformity in motion of the second shaft. 

Thus single universal joints are only used in applications where non-uniformity of rotation is acceptable. This non-uniformity can be compensated by either using two single universal joints in sequence - thus forming a universal shaft - or by using a double universal joint. 

When properly installed, the second universal joint can compensate the non-uniform rotation of the first universal joint, that is under the following preconditions, as described in DIN 808: