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Troubleshooting Double Expansion

Troubleshooting Double Expansion

Purchase Double Expansion Anchors

Problem: Inserting the wrong end of the double expansion anchor in the hole.

Trouble Shooting Tips:

  1. The double expansion anchor has an expansion nut on each end of the anchor body.  One expansion nut is threaded the other is not.  The threaded nut goes into the hole first, with the non-threaded expansion nut closest to the surface of the base material.

Problem: Getting the double expansion anchor to sit flush with the surface of the base material.

Trouble Shooting Tips:

  1. To get the double expansion anchor to sit flush with the surface of the concrete the hole must be drilled to a specific depth.
  1. Use the depth gauge on the hammer drill, if one is not available using tape to mark on the bit at the desired depth works well.
  1. To set the depth gauge or tape at the right place make sure the drill bit is in the most protracted position in the chuck and include the tip of the bit in the measurement.
  1. Setting the double expansion anchor exactly at the surface may be very difficult to do.  A deeper embedment may solve this problem and all that is requires is a longer bolt.

Problem: When turning to bolt to fasten down the item the double expansion anchor starts spinning in the hole.

Trouble Shooting Tips:

  1. Hole diameter is critical make sure that the hole size is the proper diameter for the double expansion anchor being installed.  The hole size is equal to the outside diameter of the hole.  The designated diameter is equal to the inside diameter or the diameter of the bolt that fits into the double expansion anchor.


Diameter of Double Expansion Anchor

Diameter of Hole Required

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


  1. A hammer drill must be used to ensure that the proper hole is drilled for the double expansion anchor to be installed in.  Make sure that when drilling the hole the hammer drill is set in the hammer and rotation mode.
  1. The bit must have a carbide tip and meet ANSI standards.  An ANSI standard bit ensures proper hole tolerance between anchor diameter and hole size.
  1. Make sure that the hole is clean of all dust and debris that may have been created during the drilling process.  Use a wire brush the same diameter as the hole and vacuum to remove everything from the hole.

Problem: Unable to get the bolt to engage and expand the double expansion anchor

Trouble Shooting Tips:

  1. Threads on the double expansion anchor are National Coarse Threads and will accept any bolt with national coarse threads.
  2. The two numbers designate the threads, the first number refers to the diameter of the threads and the second number is how many threads per inch.


Anchor Diameter

Type of Threads

1/4” 1/4” - 20
5/16” 5/16” - 18
3/8” 3/8” – 16
1/2” 1/2” – 13
5/8” 5/8” - 11
3/4” 3/4” - 10