A knuckle joint is a pin joint used to fasten two circular rods. In this joint, one end of the rod is formed into an eye and the other into a fork (double eye). For making the joint, the eye end of the rod is aligned into the fork end of the other and then the pin is inserted through the holes and held in position by means of a collar and a taper pin , Once the joint is made, the rods are free to swivel about the cylindrical pin.Knuckle joints are used in suspension links, air brake arrangement of locomotives, etc.