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.
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.
机用虎钳的结构及原理。机用虎钳是机械加工中常用的装夹机构，其结构如图1所示。其主要工作原理：转动方头带动丝杠，在螺母（通过紧固螺钉固定在虎钳体上）的作用下，做螺旋运动的丝杠带动与之联接的活动座沿丝杠轴线方向来回移动。
The structure and principle of machine vise. Machine vise is a common clamping mechani*** in mechanical processing. Its structure is shown in Figure 1. The main principle: rotation of the lead screw nut in the square, (fixed in the vise body through a fastening screw) under the action of moving spirally driven screw connected with the movable seat to move back and forth along the screw axis.