ASME B18 2.1 Hex Bolts is a threaded fastener with an external male thread requiring a matching pre-formed female thread such as a nut. It is invented to engage with the tool used to tighten them. Some bolt heads instead lock the bolt in place, so that it does not move and a tool is only required for the nut end. There are various types of ASME B18 2.1 Bolts such as ASME B18 2.1 carriage bolt, ASME B18 2.1 bolt, ASME B18 2.1 u-bolt, ASME B18 2.1 lag bolt, ASME B18 2.1 j-bolt, ASME B18 2.1 elevator, ASME B18 2.1 hanger bolt etc.