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.
与平键联接比较，花键联接在强度、工艺和使用方面有下列特点：在轴上与毂孔上直接而均匀地制出较多的齿与槽，故联接受力较为均匀；因槽较浅，齿根处应力集中较小，轴与毂的强度削弱较少。
Compared with the flat bond connection, the spline connection has the following characteristics in strength, process and use.More teeth and grooves are made directly and evenly on the shaft and hub hole, so the joint force is more uniform.
Because of the shallow groove, the stress at the root of the tooth is ***all, and the strength of the shaft and hub is weakened less.
花键联接按齿形的不同，可分为矩形花键和渐开线花键两类，这两类花键均已标准化。
矩形花键的定心方式为小径定心，即外花键和内花键的小径为配合面。其特点是定心精度高，定心的稳定性好，能用磨削的方法消除热处理引起的变形。
The spline connection can be divided into two types: rectangular spline and involute spline. The two kinds of spline are standardized.
The centering way of the rectangular spline is the ***all diameter centering, that is, the ***all diameter of the outer spline and the inner spline is the matching surface. It is characterized by high centering precision and good stability of centering. It can be used to remove the deformation caused by heat treatment by grinding.