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Determining Fixture Hole Diameter for Concrete Fasteners

Sunday, October 14, 2012
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The diameter of the hole in the fixture or item being attached to concrete will vary depending on the type of concrete fastener used.  It can be critically important when deciding on the diameter of the concrete anchor being used for any particular application, how the anchor will be installed and what type of expansion anchor is being used.  The fixture hole is critical only if the anchor is to be installed while the fixture or item being fastened is in place. 

Expansion Anchors
Expansion anchors all work on the same principle; it is the method of how the anchor expands that differs.  Expansion anchors work by creating an outward force against the concrete which results in creating friction. This friction provides the anchor with its holding value. 

  1. The hole in the concrete is drilled using a carbide tipped drill bit in conjunction with a hammer drill.  The diameters of the carbide tipped bits are matched tolerance with concrete fasteners and meet ANSI standards, which ensure proper tolerances.
  2. The tolerance used for carbide tipped bits and anchor diameters are not the same as the designated diameter, which is why the hole in the fixture must be slightly larger in some cases than the designated diameter. 
  3. The designated diameter refers to the thread end and not to the diameter of the working end of the anchor. To ensure that the properly threaded end dimensions are correct the working end must be slightly larger. This is why the fixture hole diameter must be calculated.

Different Expansion Methods
Concrete fasteners that use expansion to derive their holding values can be separated into three different categories:  

  • Post Expanded – anchor is installed into the predrilled hole and then expanded. As the anchor is expanded, the outward force provides the holding values.
  • Pre-Expanded –anchor is manufactured expanded and then inserted into the predrilled hole in the concrete.  Once in the hole, the steel tries pushing back to the original shape, providing an outward force and creating holding value.
  • Expanded – anchor is expanded from the inside via a nail once it is installed in the hole.

Male vs. Female Anchors
The diameter of the hole in the concrete for a male anchor is always equal to the designated diameter of the anchor being installed.  All female anchors are designated by the diameter of the bolt that can be inserted into it, with the outside diameter equal to the diameter of the hole that must be drilled. 

Type of Anchors
Concrete fasteners are manufactured in many different types that are based on expansion method and configuration.  The hole in the fixture needs to be larger only if the anchor will be installed through the fixture hole and into the masonry while the fixture is in place.

  • Wedge Anchor - post expanded,; hole needs to be larger than the diameter of the anchor chosen.
  • Sleeve Anchor – post expanded; hole needs to be larger than the diameter of the anchor chosen.
  • Strike Anchor – post expanded; hole needs to be larger than the diameter of the anchor chosen.
  • Drop-In Anchor - post expanded female anchor; the hole in the fixture does not need to be larger because the anchor is always set before the fixture in in place and the diameter of the bolt is equal to the designated diameter.
  • Metal Hit – expanded; this anchor can be placed through the hole in the fixture while the fixture is in place.  This anchor can only be installed when the fixture is in place.
  • Split Drive – pre-expanded; fixture hole needs to be larger than the nominal diameter. This type of anchor can only be installed while the fixture is in place.
  • Nylon Nail-It – expanded; always installed while the fixture is in place and will fit through a fixture hole equal to the designated diameter.
  • Lag Shield - post expanded female anchor; the anchor is always set before the fixture is set in place. The designated diameter of the anchor equals the diameter of the hole in the fixture. 
  • Single Expansion - post expanded female anchor; the designated diameter of the anchor is equal to the diameter of the hole in the fixture.  The fixture is always placed over the anchor and installed after the anchor is installed.
  • Double Expansion - post expanded female anchor; the hole drilled into the concrete is equal to the outside diameter of the anchor. The fixture is always placed over the anchor after it is installed in the masonry.  A bolt equal to the designated diameter is then inserted through the hole in the fixture.

This information is provided as a guideline when purchasing or deciding on a specific anchor for a specific application.  The optimal way to ensure that the anchor will work for any specific application is to test it by inserting the anchor through the fixture hole.

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Always use personal protective equipmentAs 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.

Article Written By:
Mike Pistorino, Vice-President Operations

 

 

 

 


Concrete Fasteners, Inc. has over 40 years of experience selling concrete fasteners. We can ship out one box or a whole pallet of concrete anchors. Our products are of the highest quality... "your satisfaction is guaranteed". We ship all orders the same day the order is received.

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