What are keybars used for? Is the role of the key bar big?

Keys are mainly used as a shaft and shaft parts of the circumferential fixation between the transmission of torque, some keys can also realize the axial fixation or axial movement of the shaft parts. Keys are divided into flat keys, half-round keys, wedge keys, tangential keys and splines. 1. The two sides of the flat key are the working surface, and there is a gap between the upper surface and the bottom of the hub groove. It has good centering performance and is easy to assemble and disassemble. Commonly used flat keys are ordinary flat keys and guide flat keys.　2. Semicircular key is also with two sides as the working surface, has good centering performance. Half-round key can swing in the shaft groove to adapt to the bottom surface of the hub groove, but the keyway of the shaft weakened, only for light load coupling.　3. The top and bottom of the wedge key is the working surface, the upper surface of the key has a slope of l:100, and the bottom surface of the hub keyway also has a slope of 1:100. When the wedge key is driven into the shaft and hub groove, its surface generates a large preload, works mainly by friction to transmit torque, and can withstand unidirectional axial force. The disadvantage is that it will force the shaft and hub to produce eccentricity, and is only suitable for the coupling with low requirements for centering accuracy, smooth load and low speed. The wedge key is divided into two types: common wedge key and hook wedge key.　4. Tangential key is composed of a pair of wedge keys, can transmit a large torque, commonly used in heavy machinery and equipment.　5. Spline is in the shaft and hub hole circumferential distribution of a number of key teeth constitute, known as spline coupling. It is suitable for centering high precision requirements, load and often slip of the joint, such as transmissions, sliding gear and shaft connection. According to the different tooth shape, spline coupling can be divided into: rectangular spline, triangular spline and involute spline. Spline linkage can be made into a static linkage, can also be made into a dynamic linkage.