Designed for use in solid concrete, brick, hollow block and solid block for medium to heavy-duty fastening.
The double expansion anchor is designed with two wedges at opposite ends of the anchor. Once a bolt is inserted and rotated, the two wedges expand the anchor body evenly outwardly against the walls of the hole in the base material. The even expansion of the anchor body eliminates high-stress points, which makes it an excellent anchor for base materials with questionable strength. The design is such that a machine bolt or a bolt with machine threads must be used. The threads on the bolt must be national coarse threads for the diameter of the anchor being used.
The double expansion anchor is made up of six parts: two halves of the anchor body, two spring bands, two wedge-shaped nuts, and one threaded with the other not threaded. Both nuts have a lug on the outside that keeps the double expansion anchor from spinning when being expanded.
The designated size of the double expansion anchor is described by the diameter of the bolt that goes into it or into the inside diameter. The double expansion anchor come in six sizes. Below is a chart showing the different sizes and the corresponding national coarse threads:
|Diameter Size||National Coarse Threads|
|1/4”||20 threads per inch|
|5/16”||18 threads per inch|
|3/8”||16 threads per inch|
|1/2”||13 threads per inch|
|5/8”||11 threads per inch|
|3/4”||10 threads per inch|
Each diameter of double expansion anchors come in one length. The length of the double expansion is measured as an overall length from one end to the other.
|Anchor Size||Length of Anchor|
A hole must be drilled into the base material and the hole size is equal to the outside diameter of the double expansion anchor. The hole must be drilled using a carbide tipped bit that meets ANSI Standards. An ANSI standard bit will ensure that the hole tolerance required for the double expansion anchor is met. The carbide tipped bit must be used in a hammer drill. It is important to remember that when the hole is being drilled that the hammer drill must be drilling in the hammer and rotation mode.
|Designated Diameter||Hole Diameter|
The depth of the hole required for the double expansion anchor is equal to the length of the specific diameter of the anchor being installed. The hole should be drilled to ensure that the top of the double expansion anchor does not protrude above the surface of the base material once it is installed. The double expansion anchor can be installed at deeper embedments, which may provide better holding values.
The double expansion anchor must be installed at a minimum depth for the anchor to obtain its minimum holding values. The minimum embedment is different for each diameter:
|Designated Diameter||Minimum Embedment|
The length of the bolt to use for any specific application is determined by adding the thickness of the material being fastened to the length of the double expansion anchor being used. Space should also be added into the bolt length for any type of washer being used or extra anchor depth
Each diameter of double expansion anchor has a corresponding part number as well as package quantity.
|Anchor Diameter||Part Number||Package Quantity|
The double expansion anchor is installed by following the steps outlined below:
As with any anchoring project, it is important to keep safety in mind and follow instructions carefully. Always remember to wear safety goggles, handle all tools with extra care and follow all technical specifications. This article is meant to serve only as a basic explanation of concrete fasteners. Always refer to manufacturer's instructions or consult a contracting expert during any anchoring project.