键是一种标准件，通常用于联接轴与轴上旋转零件与摆动零件，起周向固定零件的作用以传递旋转运动和扭矩，楔键还可以起单向轴向固定零件。而导键、滑键、花键还可用作轴上移动的导向装置。 根据键的结构形式，键联接可分为平键联接、半圆键联接、楔键联接和切向键联接等几类。

The key is a standard part, which is usually used to connect the rotating parts and swing parts of the shaft and the axle to move the fixed parts to tran***it rotary motion and torque, and the wedge key can also play a one-way axial fixation part. The guide, slippery key and the spline can also be used as a guiding device for moving on the axis. According to the structure of the key, key joins can be divided into a flat bond, a semicircle bond, a wedge bond and a tangent bond.

一个切向键只能传递一个方向的转矩，传递双向转矩时，须用互成120°～130°角的两个键。用于载荷很大，对中要求不严的场合。由于键槽对轴削弱较大 ，常用于直径大于100mm的轴上。

A tangent key can only transfer the torque of one direction. When the two-way torque is passed, the two keys of 120 to 130 degrees are required. An occasion for he***y load and no strict requirement. As the keyway is greatly weakened to the axis, it is often used on a shaft with a diameter larger than 100mm.

凡是在轴毂联接中不用键、花键或销时的联接，统称为无键联接。无键联接中我们介绍两个常用的型面联接和过盈配合联接。

The connection of no key, spline or pin in the hub connection is called the keyless connection. In keyless joins, we two commonly used type face joins and interference fit connecti***.