'''两顶尖装夹''':车削较长的轴类工件或需经过多次装夹才能加工好的工件时，为了保证每次装夹时的装夹精度，一般用两顶尖装夹。

顶尖有普通顶尖（俗称[[死顶尖]]）、[[反顶尖]]及[[活顶尖]]等。如图所示。

鸡心夹头夹持部分（或卡箍）装夹工件，另有一端与同主轴相连接的[[拨盘]]配合，主轴通过拨盘1带动紧固在轴端的卡箍2使工件转动。用两顶尖装夹工件，必须先在工件端面钻出中心孔。

[[File:搭建.jpg|缩略图|300px|[https://image.baidu.com/search/detail?ct=503316480&z=0&ipn=d&word=两顶尖装夹工件&step_word=&hs=0&pn=7&spn=0&di=38720&pi=0&rn=1&tn=baiduimagedetail&is=0%2C0&istype=0&ie=utf-8&oe=utf-8&in=&cl=2&lm=-1&st=undefined&cs=1850952209%2C2900498452&os=2900107492%2C2553903752&simid=0%2C0&adpicid=0&lpn=0&ln=385&fr=&fmq=1581415545926_R&fm=&ic=undefined&s=undefined&hd=undefined&latest=undefined&copyright=undefined&se=&sme=&tab=0&width=undefined&height=undefined&face=undefined&ist=&jit=&cg=&bdtype=0&oriquery=&objurl=http%3A%2F%2Fwww.aitmy.com%2Ffile%2Fupload%2F201407%2F24%2F21-36-08-71-1.jpg&fromurl=ippr_z2C%24qAzdH3FAzdH3Fooo_z%26e3Bwtp4y_z%26e3Bv54AzdH3FgjofAzdH3Fda89a0AzdH3Fd9AzdH3Fgjof_mbam8_z%26e3Bip4s&gsm=8&rpstart=0&rpnum=0&islist=&querylist=&force=undefined 原图链接][http://www.aitmy.com/news/201407/24/news_68061.html 来自艾特贸易]]]

[[File:仔细看真辛苦.jpg|缩略图|300px|[https://image.baidu.com/search/detail?ct=503316480&z=0&ipn=d&word=中心孔的结构&step_word=&hs=0&pn=18&spn=0&di=164340&pi=0&rn=1&tn=baiduimagedetail&is=0%2C0&istype=2&ie=utf-8&oe=utf-8&in=&cl=2&lm=-1&st=-1&cs=2372665793%2C3696006817&os=1587902670%2C133436456&simid=2571257506%2C2322961802&adpicid=0&lpn=0&ln=1621&fr=&fmq=1581415878989_R&fm=result&ic=&s=undefined&hd=&latest=&copyright=&se=&sme=&tab=0&width=&height=&face=undefined&ist=&jit=&cg=&bdtype=0&oriquery=&objurl=http%3A%2F%2Fwww.coccad.com%2FImages%2F20140305%2F20140305-02a1a80ac3d487e5e3a95f520328b1790C10405750.png&fromurl=ippr_z2C%24qAzdH3FAzdH3Fooo_z%26e3Bv5vvw1_z%26e3Bv54AzdH3Ff7k3jvpAzdH3Fwk57pAzdH3Fd0d_z%26e3Bip4s&gsm=13&rpstart=0&rpnum=0&islist=&querylist=&force=undefined 原图链接][https://coccad.com/subject/about/272.html 来自COCAD]]]

中心孔的形状有三种：A型、B型和C型，如图所示。