The concrete hole is drilled at the nominal bit diameter specified for the anchor. The hole through the steel plate, bracket or equipment base is a separate dimension and may need clearance for the anchor to pass through. Do not use a steel clearance-hole chart to choose a concrete-anchor drill diameter. For fixture holes, see the bolt hole sizes and the clearance hole sizes; for the concrete bore, use the anchor’s own instructions and the drill bit sizes.

Overall lengths differ by manufacturer, diameter and finish. Simpson’s Strong-Bolt 2, for instance, spans length codes A (1.5 in.) through T (13 in.), and catalog designations pair a diameter with a length. The examples below show how ordering designations look; they are not a complete or universal availability list.

Do not assume every diameter exists in every length, or that the same length gives the same embedment in different products. Check the exact product’s catalog.

The nut sizes and washer sizes pages give hardware heights that feed into the thread allowance, but the manufacturer’s stated fixture-thickness range for each length is what governs.

The same diameter can have several evaluated embedments, depending on anchor length, fixture thickness and the product configuration. Hilti’s KB-TZ2 data list multiple effective and nominal embedments within individual diameters. Do not publish or use a statement like “1/2 in. wedge anchor minimum embedment = X in.” Select embedment from the current technical data or evaluation report for the exact anchor system.

Hilti lists nominal and effective embedment separately for KB-TZ2. In general, nominal embedment is the installation-related depth used when drilling and setting the anchor, while effective embedment relates to the expansion mechanism and is the depth used in structural design. Do not treat anchor length, hole depth, nominal embedment and effective embedment as synonyms.

Hole depth h₀ is at least the nominal embedment, and some installation procedures call for extra depth. As one manufacturer example, Simpson’s Strong-Bolt 2 instructions say to drill to the specified nominal embedment depth, and allow drilling deeper than nominal as an alternative to cleaning, so dust has space at the bottom of the hole. That belongs to the evaluated Strong-Bolt 2 procedure; it is not a rule for every wedge anchor. Do not use a universal “hole depth = embedment + 1/2 in.” rule. Use the exact product instructions.

Fixture thickness is the thickness of the material clamped between the concrete surface and the washer and nut: a steel base plate, bracket, angle, equipment foot or railing plate. For the same diameter, a thicker fixture typically needs a longer anchor if embedment is to stay unchanged. Hilti notes that fixture thickness contributes to selecting the correct anchor length and embedment configuration.

Wedge anchors are torque-controlled expansion anchors: applying the specified torque draws the mandrel into the clip. The correct value varies with anchor diameter, material and finish, anchor system, embedment configuration and base material. Simpson states that the specific torque for Strong-Bolt 2 varies by diameter and is listed in its catalog, on a card within the box and on its website. Do not build or use a generic “1/2 in. anchor, X ft-lb” chart by mixing manufacturers. Use a calibrated torque wrench with the value for your exact product.

1. Drill: use a rotary hammer drill with a carbide-tipped bit that complies with ANSI B212.15 and has the nominal diameter specified for the anchor. Drill to the specified depth.
2. Clean: Simpson specifies blowing the hole clean with oil-free compressed air, with listed exceptions such as overhead installations and the deeper-hole alternative.
3. Drive: with the nut and washer at the top of the shaft, insert the assembled anchor through the fixture hole and drive it with a hammer until the washer and nut are firmly seated against the fixture.
4. Torque: tighten the nut to the specified installation torque with a calibrated torque wrench.

This sequence is a manufacturer example (Simpson Strong-Bolt 2) of an evaluated installation. Follow the exact instructions for your selected anchor, and do not universalize one manufacturer’s cleaning procedure.

Concrete compressive strength matters, but the effect is product- and mode-specific. Evaluated wedge anchors are typically qualified over a strength range; for example, ESR-3037 covers Strong-Bolt 2 in concrete with a specified strength of 2,500 to 8,500 psi, and ICC-ES ESR-2502 covers Power-Stud+ SD2 over the same 2,500 to 8,500 psi range. For concrete strength background, see the concrete PSI.

From 2,500 to 8,000 psi, this product’s tabulated value rises from 1,005 lb to 1,480 lb, about 47 percent. This is shown only to demonstrate that anchor capacity is not a function of diameter alone. Do not turn these numbers into a generic 3/8 in. wedge-anchor load chart.

ACI CODE-355.2-24 prescribes testing and evaluation for post-installed mechanical anchors used in structural applications under ACI CODE-318. It sets criteria for whether an anchor is acceptable in uncracked concrete only, or in cracked as well as uncracked concrete, and assigns performance categories that ACI 318 uses for capacity reduction factors and other design parameters. Do not say “all wedge anchors work in cracked concrete.”

Even within one product line, the answer changes. Under ESR-3037, Simpson’s 3/8 through 1 in. Strong-Bolt 2 anchors are installed in cracked and uncracked concrete, but the 1/4 in. size is limited to uncracked concrete, and Simpson describes its mechanically galvanized STB2-MG as tested in uncracked concrete. Seismic qualification is likewise product-specific.

• Tension: load pulling the anchor away from the concrete surface.
• Shear: load acting primarily parallel to the concrete surface.
• Combined tension and shear: both acting at once, which needs an interaction check.

ACI 355.2 covers qualification under static or seismic tension, shear and combined loading. Governing variables include the evaluated product, embedment, concrete strength and cracking, edge distance, spacing, member thickness, load direction and any reductions or interactions. A full design under ACI 318 anchoring provisions belongs to a design professional.

Anchor strength can be controlled by steel failure, concrete breakout, pullout, pryout, concrete edge breakout, tension-shear interaction and, where applicable, seismic conditions. That is why a 1/2 in. wedge anchor does not have one universal weight capacity.

Do not use a universal rule such as “edge distance = 5d.” Minimum values and strength reductions depend on the evaluated product, embedment, member geometry, loading and anchor spacing, with ACI 318 anchorage provisions applying. Use the ESR and product data for numbers.

Closely spaced anchors can have overlapping concrete breakout regions, and ACI 355.2 defines an anchor group partly by spacing relative to effective embedment. Do not apply a rule like “all wedge anchors need 6d spacing.” Spacing for foundation and sill-plate anchor bolts is a different topic; see the anchor bolt spacing for that, and use the wedge anchor’s own ESR for post-installed anchors.

Embedment cannot be chosen without considering member thickness. Simpson states that Strong-Bolt 2 is qualified for concrete thicknesses down to 3-1/4 in., and also for lightweight concrete over steel deck; that is one product’s qualification and not a universal minimum slab thickness. Reinforcement conflicts also matter; see the concrete cover chart for cover context.

Do not reduce corrosion selection to “stainless equals outdoor.” Moisture, chlorides, chemicals, contact with treated wood, interior or exterior exposure, project specifications and galvanic compatibility all matter. Zinc-plated carbon steel is not suitable for every corrosive environment.

Simpson lists applications from racking in big-box stores to resisting lateral loads from steel moment frames, and notes UL and FM approvals for its Strong-Bolt 2 where fire-suppression systems require them. DEWALT lists many similar applications for Power-Stud+ SD2. Neither list assigns a diameter by application.