An anchor bolt is 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 building to dams and nuclear power plants.

The simplest anchor bolt is a cast-in-place anchor. As seen in the figure, most designs consist of a standard bolt with a hexagonal head, which is cast in the wet concrete before it sets. There are other designs, some consisting of a bent bolt with a hook on the end, or some other sort of bending. Cast-in-place anchor bolts are the strongest type of fastener, but the casting is difficult, and they are usually only used for heavy machines mounted on poured concrete floors.

Once the concrete has been poured and set, the only other types of bolts that can be used are mechanical and epoxy bolts. Epoxy bolts are the strongest, but can be very tricky to install, since the epoxy has to be mixed to exact specifications, the hole must be very clean, and the set time has to be watched. As well, there must be a rigorous testing program. In Boston's Big Dig project, these procedures were not well carried out, which resulted in a large concrete slab crushing a motorist.

All mechanical bolts have a wedge arrangement at the end. As shown in the figure, tightening the bolt results in a wedge being driven up against a sleeve. This jams the end of the bolt, and provides the strength. Many different manufacturers provide a variation on this theme, usually depending on the condition of the concrete, and the type of load. If a mechanical anchor fails, it is usually in the form of pulling out a wedge of concrete, and for this reason, proper design looks at the depth of embedment, and assures that the bolts are not spaced too closely. In many parts of the world seismic anchors are another specialized subject. A specialized form of the anchor bolt is the rock bolt, used in rock excavations.

Nut

A nut is a type of hardware fastener with a threaded hole. Nuts are almost always used opposite a mating bolt to fasten a stack of parts together. The two partners are kept together by a combination of their threads' friction, a slight stretch of the bolt, and compression of the parts. In applications where vibration or rotation may work a nut loose, adhesives, safety pins, and other tricks are used to prevent fastener rotation. The most common shape is hexagonal, for similar reasons as the bolt head - 6 sides give a good granularity of angles for a tool to approach from (good in tight spots), but more (and smaller) corners would be vulnerable to stripping/rounding. Other specialized shapes exist for certain needs, such as wing nuts for finger adjustment and captive nuts for inaccessible areas.

Nuts are graded with strength ratings compatible with their respective bolts; for example, an ISO property class 10 nut will be able to support the bolt proof strength load of an ISO property class 10.9 bolt without stripping. Likewise, an SAE class 5 nut can support the proof load of an SAE class 5 bolt, and so on. The proof strength of the most common property classes is listed at bolted joint.