An externally threaded fastener with a hexagonal head is known as what?

A fastener characterized by external threading that features a hexagonal head is called a bolt. The design of a bolt allows it to be easily tightened or loosened using a wrench, making it a popular choice for securing parts together in various applications. The hexagonal head provides a larger surface area, which helps distribute the force applied during tightening, reducing the risk of stripping.

In contrast, a stud is typically a short length of threaded rod that is used in conjunction with a nut and does not have a head like a bolt does. A nut is a fastener that has internal threads and is used to secure a bolt or stud in place, while a washer is a flat disc that is often placed under a bolt or nut to distribute the load and protect the components being fastened. Thus, the attributes of external threading and a hexagonal head distinctly classify the fastener as a bolt.