Learning which concrete anchors are right for the job isn’t as difficult as you might think, as long as you know what the different concrete anchors are, what they do, how they do it, and why.
The Most Common Types of Concrete Anchors
- Wedge Concrete Anchor
- Drop-In Concrete Anchor
- Concrete Sleeve Anchor
- Machine Screw Anchor
- Strike Anchor
- Lag Shield Anchor
- Split Drive Anchors
The primary difference between concrete anchors is whether the anchor is male or female. Male anchors fasten to concrete via a nut and washer, and are inserted through the fixture (or object to be fastened) and into a pre-drilled hole.
Female anchors are inserted into a hole drilled into the concrete. The fixture is then placed over the hole, and a bolt is inserted through the fixture and into the hole where it is received by the anchor. A setting tool is required to spot the hole for a female anchor.
Anchors also differ by a host of other considerations. Here are the 7 most common types of concrete anchors.
1. Wedge Concrete Anchor: Named after the wedges that open and expand up to 1/16" at its base when the bolt is tightened, this male concrete wedge anchor is widely used because it is corrosion resistant, easy to insert, and among the strongest concrete anchors. It is actually a stud constructed of two adjoined pieces—one piece threaded at the top end, and the other end consisting of a mechanism that includes a clip and the wedges that expand between the stud and the wall of the hole in the concrete. Wedge anchors are usually a good option for heavy load or heavy shear applications. Heavier-duty seismic wedge anchors are used in areas frequented by seismic activity.
A couple of things to keep in mind regarding wedge anchors:
- Holes drilled into the concrete for a wedge anchor should be equal to the anchor’s diameter size.
- Wedge anchors are for solid concrete only and cannot be used in brick, block, mortar, or stone.
2. Drop-In Concrete Anchor: Sometimes confused with wedge anchors because they expand similarly, drop-in anchors are female anchors that are placed in a pre-drilled hole. The expander plug at the anchor’s base is set using a setting tool which is essentially a steel rod with one end necked down. The necked-down portion of the tool is inserted into the drop-in anchor and tapped with a hammer until the lip of the anchor meets the lip of the setting tool. Like the wedge anchor, drop-in anchors are intended for solid concrete only and can't be used effectively in brick, block, mortar, or stone.
3. Concrete Sleeve Anchor: Sleeve anchors are male fasteners that consist of a threaded bolt enveloped by an expander sleeve at the top end, and a nut and washer at the other end. The anchor is threaded through the fixture and into the pre-drilled hole in the concrete, brick, mortar, or stone. The action of turning the nut on the bolt pulls the bolt up through the sleeve, causing the sleeve to flare out up to ⅛", thereby creating the necessary hold. Sleeve anchors can be used in concrete, brick, or stone.
4. Machine Screw Anchor: A female anchor, this type of fastener consists of a cylindrical base inserted (or tapped with a hammer) into a pre-drilled hole in concrete, brick, mortar, or stone. An anchor screw is threaded through the fixture and into the hole and base. A setting tool is used to turn the screw. As the screw turns down into the base, it expands the base to secure the anchor in the hole, thereby fastening the fixture to the concrete surface. Each machine screw anchor has a specific setting tool that is determined by the diameter of the machine screw anchor being used. The anchor is properly set when the lip of the setting tool meets the lip of the anchor. Note: for machine screws, the hole size required is larger than the anchor size being used.
5. Strike Anchor (AKA hammer drive, hammer set, metal hit, or hammer drive pin anchor): This is a male fastener used to attach relatively lightweight fixtures—such as shelf brackets, conduit, and electrical boxes—to solid concrete. The strike anchor is an impact expansion fastener consisting of a tubular body capped by a drive pin that extends from the tubular casing. Once the strike anchor is inserted into the pre-drilled hole, the head of its pin is driven further into the tube via hammer strikes, expanding the tube and thereby creating the necessary hold within the hole. The diameter of the hole to be drilled for the strike anchor is the same diameter as that of the anchor to be used. Strike anchors enable long runs of fixture to be quickly installed but, once installed, are generally not removable.
6. Lag Shield Anchor: This is a female anchor consisting of a ribbed, slightly tapered sleeve of unthreaded zinc alloy that fits into a hole pre-drilled into concrete or the mortar joints of block or brick walls. As the lag screw enters and expands the sleeve, it cuts its own thread and presses the outer wall of the shield against the base material.
Lag shield anchors are generally designated as either short or long, based on the diameter of the bolt that goes into the anchor. In most cases, the long anchor shield provides better hold strength in base materials that are softer and less dense, while the shorter lag shield works best in harder or denser base materials such as masonry, where it can help to reduce drilling time.
A couple extra tips regarding lag shield anchors:
- Because of the pliability of their soft metal wedge, lag shield anchor bolts work well in situations where the hold may be subject to vibration.
- When drilling the hole for a lag shield anchor, keep in mind that proper hole size is imperative. The shield will merely spin in a hole that is too large, and if the hole is too small, the shield will be crushed by the taps of your hammer.
7. Split Drive Anchors: The resilient composition of the one-piece split drive anchor is the source of its holding power. Made of tough carbon steel, split drives are male anchors that have an expanded base that is split. While the split base is compressed as the anchor is hammered into the pre-drilled hole, it maintains outward pressure on the walls of the hole, giving the split drive anchor its holding power.
More tips for installing split drive anchors:
- The hole size should be equal to the diameter of the base of the anchor.
- Split drive anchors are intended for light-duty anchoring to concrete, brick, or block.
See the chart below to assist you in selecting the best concrete anchor for your project.
V = Very suitable M = May be suitable
| Type of Material | Soilis Concrete | Hollow Concrete Block | Grout Filled Block | Brick | Mortar |
|---|---|---|---|---|---|
| Wedge Anchor | V | M | |||
| Sleeve Anchor | V | V | V | V | V |
| Drop-In Anchor | V | M | |||
| Machine Screw Anchor | M | V | M | V | V |
| Leadwood Screw Anchor | V | V | V | V | |
| Single Expansion Anchor | M | M | V | V | V |
| Double Expansion Anchor | M | M | V | V | V |
Other Considerations in the Selection of the Right Concrete Anchor
Rust and Corrosion
Anchors composed of stainless steel are the most rust resistant, and should be used if the anchor will be submerged in water, or subject to occasional wet conditions outdoors. Zinc-plated anchors can be used outdoors, but will rust eventually. For dry, indoor use, standard zinc-plated anchors will suffice.
Load Requirements
Load consists of pressures on the concrete relative to the item being fastened to it. The anchor must be able to withstand the load factors of shear and tension. Anything fastened to concrete bears weight, referred to as “load.” The chart below is intended for general reference regarding load values, and should be used in conjunction with specific load data from the fastener manufacturer.
Ultimate Load Values in 2,000 psi Concrete
| Size | Min. Embedment | Drill Bit | Pull-out (lbs) | Shear (lbs) |
|---|---|---|---|---|
| 1/4" | 1-1/8" | 1/4" | 877 | 1082 |
| 5/16" | 1-1/8" | 5/16" | 892 | 1156 |
| 3/8" | 1-1/2" | 3/8" | 1525 | 3238 |
| 1/2" | 2-1/4" | 1/2" | 2999 | 5564 |
| 5/8" | 2-3/4" | 5/8" | 3749 | 6198 |
| 3/4" | 3-1/4 | 3/4" | 4978 | 9378 |
| 7/8" | 3-7/8" | 7/8" | 6294 | 13687 |
| 1" | 4-1/2" | 1" | 7329 | 17712 |
| 1-1/4" | 5-1/2" | 1-1/4" | 13162 | 24206 |
Weights
Generally, smaller objects that weigh less can be fastened using 3/16" and 1/4" diameter fasteners. Medium weight items should be sufficiently served by ⅜", 1/2", or ⅝" diameter fasteners, while ⅝", ¾", or 1" diameter fasteners work best for heavy objects.
Concrete anchors and fasteners can be used in various concrete applications and projects. Before installing any concrete anchors, it is important to know the differences among concrete anchors and their applications so you can select the best one for the job.
Product Compliance and Suitability
The product statements contained in this guide are intended for general informational purposes only. Such product statements do not constitute a product recommendation or representation as to the appropriateness, accuracy, completeness, correctness or currentness of the information provided. Information provided in this guide does not replace the use by you of any manufacturer instructions, technical product manual, or other professional resource or adviser available to you. Always read, understand and follow all manufacturer instructions.