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。Thekeyisastandardpart,whichisusuallyusedtoconnecttherotatingpartsandswingpartsoftheshaftandtheaxletomovethefixedpartstotran***itrotarymotionandtorque,andthewedgekeycanalsoplayaone-wayaxialfixationpart.Theguide,slipperykeyandthesplinecanalsobeusedasaguidingdeviceformovingontheaxis.Accordingtothestructureofthekey,keyjoinscanbedividedintoaflatbond,asemicirclebond,awedgebondandatangentbond.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。Thesplineconnectioncanbedividedintotwotypes:rectangularsplineandinvolutespline.Thetwokindsofsplinearestandardized.Thecenteringwayoftherectangularsplineisthe***alldiametercentering,thatis,the***alldiameteroftheoutersplineandtheinnersplineisthematchingsurface.Itischaracterizedbyhighcenteringprecisionandgoodstabilityofcentering.Itcanbeusedtoremovethedeformationcausedbyheattreatmentbygrinding.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。Thestructureandprincipleofmachinevise.Machineviseisacommonclampingmechani***inmechanicalprocessing.ItsstructureisshowninFigure1.Themainprinciple:rotationoftheleadscrewnutinthesquare,(fixedinthevisebodythroughafasteningscrew)undertheactionofmovingspirallydrivenscrewconnectedwiththemovableseattomovebackandforthalongthescrewaxis.)