COTTER JOINT A cotter joint is used to connect rigidly two co-axial rods or bars which are subjected to axial tensile or compressive forces . It is a temporary fastening . COTTER A cotter is a flat wedge shaped piece of rectangular cross section and its width is tapered (either on one side or on both sides) from one end to another for an easy adjustment. APPLICATIONS OF COTTER 1. Connection of the piston rod with the cross heads 2. Joining of tail rod with piston rod of a wet air pump 3. Foundation bolt 4. Connecting two halves of fly wheel (cotter and dowel arrangement) COMPARISON BETWEEN KEY AND COTTER 1. Key is usually driven parallel to the axis of the shaft which is subjected to torsional or twisting stress. Whereas cotter is normally driven at right angles to the axis of the connected part which is subjected to tensile or compressive stress along its axis. 2. A key resists shear over a longitudinal section whereas a cotter resist shear over two transverse section.