A hanger bolt is a cylindrical metal fastener that is threaded at both ends and often tapered at one end. Hanger bolts are driven into hard surfaces with drills and hammers so that one of the threaded ends is left protruding. Nuts and other hanging accessories are secured to a hard surface by twisting them onto the exposed threads of the hanger bolt. Steel hanger bolts with a wider diameter and increased length have greater sheer strength, which allows them to support the weight of heavier objects. Sheer strength is the ability of a component to withstand force without breaking.
Hanger bolts that are designed to be screwed in have an indentation in one end where a square or hexagonal bit can be inserted. A hammer-driven hanger bolt has a flat end to strike and a tapered end to push into the mounting surface. Driving a hanger bolt too far into the hard surface may make it impossible to properly attach the hanging hardware. A hanger bolt is more likely to come out, bend, or snap when less than half of its length is plunged into the hard surface. Stainless and galvanized steel hanger bolts prevent rust and are commonly suggested for outdoor hanging applications.
Commercial and home craftsman often choose a sturdy hanger bolt to connect two surfaces and fully hide the fastener. Once the hanger bolt is driven into the wall, the other end disappears into the backside of the hanging piece. This flush mounting technique makes the mounted item appear to be floating in place on the surface without any visible support. Some large objects require several hanger bolts driven at equal depths along their length to keep them from pulling out of the hard surface and coming down. The stability of the mount is only as secure as the weakest hanger bolt.
Specialized hanger bolts are made for a variety of mounting jobs and surfaces. Some custom-designed hanger bolts have anchoring systems that help hold them in place once they are installed. These anchoring hanger bolts are commonly driven into thinner and less sturdy materials like drywall and woods to increase the stability of the mount. Spring-loaded hanger bolts pop open once inside the mounting surface to make it even more difficult to pull them out. It can be difficult to remove some types of hanger bolts without causing noticeable damage to the mounting surface.