 Welcome back MechanicalEI, did you know that tie rods and tension links in bridge structures that help the bridge stand make use of knuckle joints? This makes us wonder, what is a knuckle joint? Before we jump in, check out the previous part of this series to learn about what a lathe is. First, let's find out what is a key. A key is used to connect a rotating machine element to a shaft. It prevents relative rotation between two parts and may also enable torque transmission. Parallel keys have a square or rectangular cross section. Square cross sections are used for smaller shafts and rectangular cross sections are used when the wall thickness of the mating hub is constrained. Feather keys are similar to parallel keys except they are radius on both ends and machined to tight tolerances. Woodref keys are semi-circular, fitting partly into a circular segment keyway with the remainder fitting into a longitudinal slot keyway in the mating part. Parallel, woodref and feather keys are all types of sunk keys. Lastly, saddle keys are the keys that are attached to the driving member and are used to transmit power to the driven members like couplings. Now, a knuckle joint is used to connect two rods under tensile load. The joint permits angular misalignment of the rods and may take compressive load if it is guided. In this type of joint, one of the rods has an eye at the rod end and the other is forked with ice at both the legs. A pin called knuckle pin is inserted through the rod end eye and forked eyes. It is secured by a collar and a split pin. Knuckle joint can withstand large tensile loads and has good mechanical rigidity. It is easy to manufacture and set up. However, it cannot withstand large compressive loads and permits angular momentum in only one plane. Hence, we first saw what different types of keys are and then went on to see what knuckle joint is. So, like, subscribe and comment with your feedback to help us make better videos. Thanks for watching. Also, thanks a lot for those constructive comments. You helped the channel grow. So, here are the top mechanical EIs of our last videos. In the next episode of Mechanical EI, find out what couplings are.