A bolt is a mechanical fastener with a threaded shaft. Bolts are closely related to screws, which are also mechanical fasteners with threaded shafts. These types of fasteners are typically inserted through two parts, with aligned holes.
According to some definitions, whether something is a bolt or a screw depends on how it is used. A bolt is inserted through parts which all have unthreaded holes and a nut is then screwed onto the bolt to provide a clamping force and prevent axial movement. A screw may first pass through a first part with a clearance hole but its threads mate with threads in one of the parts being fastened. A screw may cut its own threads or mate with a threaded part.