A knuckle joint is a mechanical joint used to connect two rods which are under a tensile load, when there is a requirement of small amount of flexibility, or angular moment 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 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. Connecting rods between locomotive wheels. Design of knuckle joint REF. The assembly diagram of knuckle joint is as shown in fig. The dimension of knuckle joints are: Diameter of rod = d Diameter of knuckle pin = dp Outside diameter of single eye = doe Outside diameter of double eye = dod Thickness of single eye = t Thickness of fork = t1 Axial tensile force on rod = P (1) Diameter of rod Consider the rod is subjected to a direct tensile stress ς = P / π d2 From above equation, diameter of rod 'd' is obtained. (2) Design of pin (dp) (a) Consider the failure of pin under double shear due to tensile force. Therefore, direct shear stress induced in knuckle pin is given by Equation ς = P / 2A = (P/2) / (π/4) dp2 = 2P / π dp2 (b) Failure of knuckle pin in bending Assume there is no clearance or slack but in actual, knuckle pin is loose in forks to permit angular moment of one with respect to other, so it is subjected to