ANS:B - Stud

The fastening device that has a head at one end and a nut fitted to the other end is called a Stud. A stud is a threaded rod with threads on both ends. One end is typically designed to have a head, which may be hexagonal or another shape, allowing for easy turning with a wrench or socket. The other end of the stud is left unthreaded or partially threaded to accommodate a nut. When used in assembly or construction, one end of the stud is inserted into a pre-drilled hole in one of the components to be joined, and the nut is then screwed onto the other end to secure the components together. Studs are commonly used in applications where one of the components being fastened is too thin to accommodate a bolt with threads extending beyond the thickness of the material. Therefore, the correct answer is Stud.