A fastener is a hardware device that mechanically joins or affixes two or more objects together. In general, fasteners are used to create non-permanent joints; that is, joints that can be removed or dismantled without damaging the joining components. Welding is an example of creating permanent joints.
An anchor bolt is a fastener used to attach objects or structures to concrete. There are many types of anchor bolts, consisting of designs that are mostly proprietary to the manufacturing companies. All consist of a threaded end, to which a nut and washer can be attached for the external load. Anchor bolts are extensively used on all types of projects, from standard buildings to dams and nuclear power plants.
A wall plug (UK English), also known as an anchor (US English), is a fiber or plastic (originally wood) insert used to enable the attachment of a screw in material that is porous or brittle or that would otherwise not support the weight of the object attached with the screw. It is a type of anchor that, for example, allows screws to be fitted into masonry walls.
A screw is a type of fastener, sometimes similar to a bolt (see Differentiation between bolt and screw below), typically made of metal, and characterized by a helical ridge, known as a male thread (external thread) or just thread.
A nut is a type of fastener with a threaded hole. Nuts are almost always used in conjunction with a mating bolt to fasten multiple parts together. The two partners are kept together by a combination of their threads' friction (with slight elastic deformation), a slight stretching of the bolt, and compression of the parts to be held together.
In applications where vibration or rotation may work a nut loose, various locking mechanisms may be employed: lock washers, jam nuts, specialist adhesive thread-locking fluid such as Loctite, safety pins (split pins) or lockwire in conjunction with castellated nuts, nylon inserts (nyloc nut), or slightly oval-shaped threads.