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Large Diameter Tapcons

Published by Robert Carlisle on Feb 28th 2009

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Large diameter Tapcons received their name based on their size. These Tapcons are larger in diameter than the standard Tapcon®. Large diameter Tapcons are manufactured by ITW Red Head, which is the same manufacturer that produces the standard blue Tapcon®. Other manufacturers offer similar products. Simpson Strong-Tie calls their large diameter Tapcons the Titen-HD® while Power Fasteners has named their LDT (Large Diameter Tapcon®) the Wedge Bolt®.

The large diameter Tapcon® is available in numerous diameters of 3/8", 1/2", 5/8", and 3/4" with different lengths for each diameter to meet numerous application requirements. The LDT allows for higher loads in shallower embedments. They can be set closer together and further from unsupported edges than standard mechanical type concrete fasteners. Unlike the standard Tapcon® that only has 1-3/4" of threads, the large diameter Tapcons are fully threaded to provide higher pullout resistance and better engagement of the threads. Compared to other mechanical type concrete anchors, large diameter Tapcons are easier to install, do not require any nuts & washers, are easily removed and have a finished look once set in place. Large diameter Tapcons are approved by the City of Los Angeles and have Miami-Dade approval that complies with high-velocity hurricane zone requirements ( #04-1025.8).

Large diameter Tapcons are only available in a hex washer head and are not manufactured with a flat countersunk head. The size of the hex washer head varies depending on the diameter of the LDT being used. The 3/8" diameter requires a 9/16" socket, the 1/2" requires a 3/4" socket, the 5/8" and 3/4" both require a 15/16" socket. The diameter of the hole in the fixture must be larger than the diameter of the large diameter Tapcon® being used.

Below is a chart containing the fixture hole requirements for the various diameters of large diameter Tapcons:

LDT Diameter
Fixture Hole

Large diameter Tapcons are made from hardened, carbon grade 5 steel that is zinc plated or coated with an Envirex® corrosion resistant coating. The zinc plated large diameter Tapcons should not be used with any type of treated lumber. The Envirex® coated LDT has been deemed appropriate for use with treated lumber. The Envirex® coated Tapcons are only available in the 3/8" and 1/2" diameters. Any excessive content of copper in the ACQ or MCQ treated lumber may affect the finish of the LDT. These Tapcons are also available in 410 stainless steel.

These Tapcons have an extra large hex washer head that increases bearing surface with the fixture being fastened. The anti-rotation washer attached to the head of the LDT is serrated to prevent it from backing out. The head of these Tapcons is plainly marked with a length identification letter, which allows for embedment depth inspection after the anchor is set.

Each diameter of the large diameter Tapcon® can be used in concrete and grout-filled CMU. The 3/8" diameter Tapcon® is the only one that can be used in hollow CMU. Requirements for proper installation of an LDT include: proper bit size, required socket size, minimum embedment and hole depth.

Below is a chart describing important information for each diameter of LDT:

  Bit Diameter   Minimum Hole
LDT Diameter ANSI Standard Socket Size Embedment Depth
3/8" 5/16" 9/16" 1-1/2" 2-1/2"
1/2" 7/16" 3/4" 2-1/2" 3-1/2"
5/8" 1/2" 13/16" 2-3/4" 3-3/4"
3/4" 5/8" 13/16" 3-1/4" 4-1/4"

The performance of these Tapcons is dependent on a number of different factors including the diameter of the anchor being used and the depth of embedment. Generally, the larger the diameter- the deeper the embedment- the better the holding values. Two different factors that will decrease the holding values of an LDT is the space between anchors and the distance from an unsupported edge. To achieve maximum working loads for tension, these anchors should be a minimum distance away from each other. These distances are as follows: 6" for the 3/8" and 8" for the 1/2". Minimum spacing requirements are 3" for both the 3/8" and 1/2" and the holding values for tension loads should be reduced by 70% for the 3/8" and 27% for the 1/2". The minimum edge distance for a tension load is 1-3/4" and the minimum load factor should be reduced by 70% for the 3/8" diameter and 65% for the 1/2" diameter anchor.

The maximum working tension load varies with different embedment depths. A 3/8" diameter at 1-1/2" and 2" embedment should be placed a minimum of 2" from any unsupported edge to achieve a maximum working load. Embedment depths of 2-1/2" and 3-1/2" need 3" and 4" respectively to achieve maximum tension working load. The 1/2" diameter at 2", 3-1/2" and 4-1/2" embedment derives the maximum tension working load from an unsupported edge at 2-1/4", 3" and 4" respectively.

If an LDT is placed in lightweight concrete, the edge and .75 should divide spacing distance and linear interpolation can be used for spacing and edge distance requirements. For the 5/8" and 3/4" Tapcons, the critical edge distance should be 10 times the anchor diameter. If the minimum edge distance for the 5/8" and 3/4" is reduced to 1-3/4" then the load factor for tension loads of 0.65 is used and a 0.15 load factor is used for shear loads when applied perpendicular to the edge. If the load is parallel to the edge, a load factor of 0.60 must be used. For shear loads, the recommended edge and spacing requirements are different than tension loads. To achieve maximum shear working loads, the edge distance for the 3/8" range range for 3" to 5" depends on the embedment depth. For the 1/2", the maximum shear loads distance is 5" to 5/12". At a minimum distance of 1-3/4" from an unsupported edge, the load factor is 25% for both diameters. Just as with tension loads, .75 should be subtracted in lightweight concrete.

Installation of large diameter Tapcons is simple and can be accomplished in two steps. The process is different when installing large diameter Tapcons into concrete and concrete block (CMU).

Below is the installation steps for both applications:

Installation of Large Diameter Tapcons in Concrete

1. Using a hammer drill and the properly sized carbide bit, drill a hole in the concrete a minimum of 1" deeper than the large diameter Tapcons being embedded.

2. Insert the LDT being used through the fixture and into the hole in the concrete. With a socket wrench or an electric impact wrench, tighten the anchor until it is completely seated.

Installation of Large Diameter Tapcons in Concrete Block (CMU)- 3/8" and 1/2" diameter only

1. With the proper diameter of carbide bit for the LDT being installed, drill a hole in the concrete brick using a hammer drill. Is is important that the hole is 1" deeper than the anchor being embedded.

2. Place the LDT through the fixture hole and into the hole drilled in the base material/concrete block. Using a socket wrench, tighten by hand until the Tapcon® is snug against the fixture being fastened. Do NOT use an electric impact drill when using an LDT in block base material.

Large diameter Tapcons are strong, versatile anchors that can be used in various applications. It is important to consider holding values, embedments and spacing requirements before installing a large diameter Tapcon®.

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