Types of Expanding Bolts

Written by damon hildebrand
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Types of Expanding Bolts
Expansion bolts anchor fixtures and building material to concrete and solid structures. (bolt image by Grebenshchikov from Fotolia.com)

Expansion bolts come in various shapes, sizes and materials. Used for attaching fixtures to a permanent surface, the type and size of expansion bolts is determined by the specific application. All expansion bolt anchors require a hole drilled into the material in which the anchor will be attached. The size of the hole is generally the same size--or slightly smaller--than the diameter of the expansion bolt anchor. This ensures the anchor has ample room to expand and lock itself into the wall or floor where it is installed.

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Plastic screw anchors are for use in hollow walls and ceilings. The drywall or plaster material of the wall is not strong enough to support a nail or screw for hanging objects more than 454 or 907g. The plastic expansion anchor is inserted into the pre-drilled hole. Screwing the bolt or screw into the plastic anchor causes the anchor to expand. The expanded anchor serves as a solid anchor point for a picture, mirror or other decorations.


Sleeved expanding anchor bolts are for fastening fixtures to solid material such as wood, brick or concrete. A sleeve anchor is a threaded bolt with a nut on one end and a cone shape on the opposite end. A metal sleeve surrounds the bolt, resting between the nut and cone. After inserting the sleeve anchor into the pre-drilled material, tightening the nut draws the cone and nut together. The metal sleeve expands between the nut and cone--anchoring the sleeve bolt into the solid base material.


A wedge-type expanding bolt works in a similar manner to the sleeve-type. A wedge anchor bolt has threads at one end and is plain at the other. A carbon steel clip permanently attaches near the end of the unthreaded section. When connecting a piece of building material--such as a wood beam to concrete--the anchor wedges itself into the concrete's pre-drilled hole as the bolt's nut is tightened. Room additions often use wedge-type expanding bolts when attaching new wall footers to the concrete slab.


Manufactured from soft metal such as aluminium, drop-in expansion bolt anchors use machine screws as their fastener. Inserted into a tight fitting, pre-drilled hole in masonry or solid wood, the fastener is removable from the drop-in anchor after the anchor is set. As the machine screw tightens, the entire body of the aluminium anchor expands against the inside of the pre-drilled hole.

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