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Tips and Tricks Double Expansion Anchor

Installing Double Expansion Anchors: Step-by-Step Instructions

Purchase Double Expansion Anchors

Hand railings are essential safety features for many stairwells. When installing hand railings, it is extremely important that the railing is sturdy, safe, and secure. If the handrail is to be installed onto a brick wall, many contractors use the double expansion anchor.

Double Expansion Anchor

The double expansion anchor is great for projects where the base material is softer or has the strength that is suspect.

The anchor body is made from a die cast alloy called Zamac, which is rust resistant and extremely durable. It has two expansion cones—one cone is threaded and the other is not. Two spring steel bands wrap the two halves together and allow the anchor to expand once installed.

Safely Install the Anchor

1. Preparing

  • A hole will need to be created in the base material. This is where the anchor will be inserted and installed.
  • Drilling into masonry materials requires the use of a hammer drill. A hammer drill breaks up the base material with an up and down hammering motion while the rotation removes the dust. A straight rotation drill should not be used because the hole created will not meet the standards required for the anchor.
  • Along with the hammer drill, a carbide tipped bit meeting ANSI standards must be used. ANSI standards ensure that the carbide bit meets the hole tolerance required for the anchor.
  • Anchors sizes are designated by the inside diameter. The hole diameter requirement is equal to the outside diameter of the anchor.

Double Expansion Anchor Hole Requirements

Designated Diameter

Hole Diameter

1/4” 1/2”
5/16” 5/8”
3/8” 5/8”
1/2” 7/8”
5/8” 1”
3/4” 1-1/4”


2. Drilling

  • The depth of the hole in the base material must be at a minimum equal to the length of the anchor that is being installed.
  • In many scenarios, a deeper embedment will provide better holding values but will also require a longer bolt.
  • The depth gauge provided with the hammer drill can be used to ensure proper hole depths. If a depth gauge is not available, wrap tape around the bit at the embedment depth required. If the hammer drill being used is a keyless chuck type, make sure that the bit is in the most retracted position to ensure proper hole depth.
  • Carefully drill the hole

3. Cleaning

  • Cleaning the hole of all dust and debris before installing the anchor is critical to ensure proper holding values. Use a wire brush in an up and down motion and a turning motion. Then vacuum to clean out the hole. Compressed air can be used in some projects, but often the dust created will prohibit its use.

4. Installing

  • The length of the bolt that should be used for all installations of the anchor is equal to the thickness of the material being fastened plus the depth the anchor will be embedded.
  • It is important to note that one end of the double expansion anchor has a nut that is threaded. When installing it, hold the opposite end or the end with the nut that is not threaded and insert the threaded nut end into the hole first. Tap lightly with a hammer if needed until the anchor is flush with the surface of the base material.
  • Take the fixture being fastened and align the holes in the fixture with the double in the base material.
  • Insert the national threaded bolt through the fixture and into the anchor. Turn the bolt clockwise until the anchor is fully set. Do not over torque the bolt since this may cause the double expansion anchor to spin in the hole and lose its holding strength.