movement is necessary. There is always axial or linear line of action of load. The knuckle joint assembly consists of the following major components: Single eye. Double eye or fork. Knuckle pin. At one end of the rod the a single eye is formed and a double eye is formed at the other end of the rod. Both, single and double eye are connected by a pin inserted through the eye. The pin has a head at one end and at other end there is a taper pin or split pin. For gripping purpose, the ends of the rod are of octagonal forms. Now, when the two eyes are pulled apart, the pin holds them together. The solid rod portion of the joint in this case is much stronger than the portion through which the pin passes. The modes of failure are: Shear failure of pin (single shear). Crushing of pin against rod. Tensile failure of flat end bar. Application: Tie rod joint of roof truss. Tension link in bridge structure. Link of roller chain. Tie rod joint of jib crane. The knuckle joint is also used in tractor. Turnbuckle The buckle or a coupler is a mechanical joint used to connect two members which are subjected to tensile loading which require slight adjustment of length or tension under loaded conditions. It consists of central hexagonal nut called coupler and tie rod having right-hand and left-hand threads. A coupler of hexagonal shape is to facilitate the turning of it with a spanner or sometime a hole is provided in the nut so that a tommy bar can be inserted for rotating it. As the coupler rotates, the tie rods are either pulled together or pushed apart depending upon the direction of the rotation coupler. Normally the tie rods are made of steel, while the coupler is made of steel or C.I. Application : To tighten the members of the roof truss. Used to connect link in a mechanism to transfer motion. Used between the two railway wagon or bogies. To tighten the cable or stay ropes of electric distribution poles. Cotterpin This is mainly used to connect rigidly two rods which transmit motion in the axial direction, without rotation. These joints may be subjected to tensile or compressive forces along the axes of the rods. The very famous example is the joining of piston rod's extension with the connecting rod