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Expansion Fasteners

Expansion anchors are for solid core material like concrete (or brick, stone, and mortar). They work by transferring the tension or pulling force on the bolt into the concrete through friction or expansion pressures.

The base of the fastener is designed to expand against the sides of the hole in any number of ways dependent upon the type of fastener selected.

Here are some examples:

• Wedge fastener This system uses a nut, washer and a steel stud bolt which has a tapered mandrel at the bottom. Surrounding this mandrel is either a steel clip or separate steel wedges. When the nut is tightened the mandrel is drawn up into the clip or wedges forcing them to become wedged between the mandrel and the sides of the hole.
• Sleeve fastener The sleeve expansion fastener has a nut, washer, steel stud bolt and a sheet metal expansion sleeve. As in the wedge expansion fastener, the bottom of the bolt has a uniformly tapered mandrel of the same diameter as the expansion sleeve. The sleeve itself is slit lengthwise to aid in expansion. When the nut is tightened it draws the mandrel into the sleeve forcing it to expand and bear against the sides of the hole.
• Stud fastener In contrast to the Wedge and Sleeve fasteners which use a tightened nut to cause expansion of the fastener against the sides of the hole, the stud fastener is expanded by hammering upon the top of the stud. The stud expansion fastener is threaded at the top end and has a drilled hole with vertical slits at the bottom end of the stud. This hole at the bottom of the stud sits over a tapered steel plug. When the top of the stud is hammered, the bottom of the steel stud is forced over tapered steel plug which results in an expansion of the steel stud against the sides of the hole.
• Self-drilling fastener Rather than being set into a predrilled hole, the self-drilling fastener has teeth for cutting its own hole in the concrete. This fastener is comprised of a steel shell (with teeth) and a tapered steel plug. The top of the shell is internally threaded so a bolt can be screwed into it. By hammer drilling the shell over the tapered steel plug, the bottom the shell is forced to expand and bear against the sides of the hole.
• Drop-in fastener This system uses a steel shell and an internal steel expander plug.

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