A diagram of a carriage bolt.
<ol><li>Bolt head</li>
<li>Round part</li>
<li>Square part (or carriage)</li>
<li>Bolt threads</li></ol>
<a href="//commons.wikimedia.org/wiki/User:Andrew_c" title="User:Andrew c">Andrew c</a>
<span class="int-own-work" lang="en">Own work</span>