Universal Joints

Ball and Socket joints provide great deal of flexibility, however when it requires to apply force to transferring torque it cannot achieve maximum output. For example lifting/ turning of something a rigid rod that allows the rod to 'bend' in any direction, and is commonly used in shafts that transmit rotary motion. It requires a rigid member (rod) connecting to a shaft so that the force is converted to rotate. Basically when one moves the other has to remain rigid so that the torque can translate the rotational movement. It has wide range of applications.

6A Hooke’s Joint	6B Universal Joint link	6C Car Axel	6D Car Jack

(Source: http://www.google.co.in/search?um=1&hl=en&q=Universal+Joints&bav=on.2,or.r_gc.r_pw.r_qf.
&biw=1332&bih=581&ie=UTF8&tbm=isch&source=og&sa=N&tab=wi&ei=NsJSUOw6yKusB9ekgZgD#
um=1&hl=en&tbm=isch&sa=1&q=Universal+Joints+in+automobile&oq=Universal+Joints+in+automobile
&gs_l=img.12...97434.103191.0.105034.14.13.0.0.0.0.0.0..0.0...0.0...1c.1.TfF7lV-YLuY&pbx=1&bav=on
.2,or.r_gc.r_pw.r_qf.&fp=a6e072f013c9232b&biw=1332&bih=581 ; Sept. 14, 2012)
(Read more: http://en.wikipedia.org/wiki/Universal_joint ; Sept. 14, 2012)

The Hooke’s joint (plate 6A) or coupling is connected to two members A&B. ‘A’ is a static rod that rotates the ‘B’ rod. The rotation of the ‘A’ rod allows the rod to 'bend' in any direction and is commonly used in shafts that transmit ‘rotary motion’. Therefore universal joint (plate 6B) has two parts one rigid and the other one rotary. Automobile axel (plate 6C) applies universal joint to generate rotary motion with the help of universal joints. Automobile jack (plate 6D) has similar application that requires vertical movement for lifting the car above the ground.