Anchor fasteners fall into five main groups: cast-in-place bolts, mechanical expansion anchors, hollow-wall anchors, plastic expansion anchors, and chemical anchors.
Choosing the right anchor fastener is the difference between a shelf that stays up for a decade and a television on the floor. Whether you’re hanging a cabinet on drywall or bolting machinery to concrete, the wrong choice fails—sometimes catastrophically. Selection comes down to two questions: what is your base material, and how much weight are you supporting?
Cast-In-Place Anchor Bolts: Set Before The Concrete Cures
Cast-in-place anchor bolts are placed into wet concrete and left to cure, becoming a permanent part of the foundation. Common examples include L bolts and J bolts, named for the bent shapes at the embedded end that resist pull-out forces.
These anchors offer the strongest possible connection to concrete because the bond forms during curing rather than relying on mechanical expansion. You will find them securing structural steel columns, heavy equipment, and building frames. The tradeoff is planning: once the concrete cures, you cannot reposition the bolt. Hilti’s technical literature groups these separately from post-installed systems—their installation window closes when the concrete sets.
Mechanical Expansion And Impact Anchors: Post-Installed Options
Mechanical expansion anchors install into pre-drilled holes in cured concrete and grip the base material by expanding against the hole walls. Wedge anchors, sleeve anchors, and drop-in anchors are the most common types.
Wedge anchors are heavy-duty fasteners made from galvanized carbon steel with a nut and washer; lower-cost versions use zinc-plated steel. You drill the base, insert the anchor, and tighten the nut so the clip at the bottom expands and grips the concrete. Sleeve anchors work similarly—drill, insert, and tighten so the sleeve expands against the masonry.
Impact or set anchors take a different approach. Hammer drive anchors are driven into a pre-drilled hole, and striking the pin expands the sleeve to lock the anchor in place. They are light-duty fasteners for concrete, brick, or block and are generally not removable once installed. Split drive anchors work the same way and suit the same light-duty jobs.
For drop-in anchors specifically, a sound, fully cured base material is mandatory—they are not a substitute for cast-in-place bolts. If the concrete is cracked or weak, the expansion cannot develop its holding force properly.
Hollow-Wall And Plastic Anchors: Light-Duty Options For Drywall And Block
Hollow-wall anchors solve a different problem: gripping material with empty space behind it. Toggle bolts are the classic solution—you insert the bolt and spring-loaded wings through a hole in the drywall, and tightening pulls the wings open flat against the back side of the wall surface. They are excellent for hollow walls but completely wrong for solid concrete or masonry.
Molly or hollow wall anchors are the other common type. The serrated sleeve collapses against the back of the drywall as you tighten the screw, spreading the load across the wall surface. Plasterboard anchors are the lightest option, fine for small pictures and light hooks.
Plastic expansion anchors sit between the hollow-wall and heavy-duty categories. These plastic sleeves expand when you drive a screw into them, providing a snug grip in solid materials like block, brick, or concrete. They are strictly light-duty—fine for cable clips and small fixtures, not for anything load-bearing.
Chemical Anchors: Bonded Strength For Heavy Loads
Chemical anchors use resin or adhesive to bond a threaded rod or stud into a drilled hole. You drill and clean the hole, inject the resin, then place the threaded rod; the connection develops full strength after the adhesive cures. Common versions include chemical anchor studs, bolts, and rods.
Chemical anchors excel where mechanical expansion anchors struggle—close to edges, in cracked concrete, or overhead. Hilti’s technical literature lists anchor rods like the HAS-U in strength classes 5.8 and 8.8, along with the AM rod in 8.8, showing the range of load capacities. The HIS-N is an internally threaded chemical anchor system used where you need to attach a bolt later.
These anchors demand careful installation. The hole must be drilled to the right diameter and depth, cleaned thoroughly of dust, and filled with the correct adhesive for the base temperature and material. For load-bearing use, follow the product manual and the applicable approval, such as the European EAD 330499 for bonded fasteners or EAD 330232 for mechanical fasteners. Improper cleaning or curing can reduce the anchor’s holding power dramatically.
| Anchor Type | Best For | Key Limitation |
|---|---|---|
| Cast-in-place (L, J bolts) | Structural steel, heavy equipment in wet concrete | Must be placed before concrete cures |
| Wedge anchors | Heavy loads in solid cured concrete | Requires sound, crack-free base material |
| Sleeve anchors | Medium-heavy loads in concrete or masonry | Holding power depends on expansion force |
| Hammer/split drive anchors | Light fixtures in concrete, brick, block | Not removable once installed |
| Toggle bolts | Hollow walls (drywall, plaster) | Useless in solid concrete or masonry |
| Molly anchors | Medium loads in hollow walls | Requires correct hole size to grip |
| Plastic expansion anchors | Light duty in solid materials | Not for load-bearing applications |
| Chemical anchors | Heavy loads, cracked concrete, edge proximity | Demands precise drilling, cleaning, curing |
If you are planning a specific project and want to compare rated options side by side, our tested roundup of the best anchors and fasteners on the market covers real-world performance across these categories. Hilti’s anchor systems technical guide offers the authoritative engineering detail, including load tables and approval documents.
The right anchor comes down to base material and load. For wet concrete, cast-in-place bolts win. For cured concrete with heavy loads, choose wedge or chemical anchors. For drywall, toggle bolts are the reliable pick. Match the anchor to the job, follow the installation steps, and the connection will hold for years.
References & Sources
- Hilti Anchor Systems. Technical Literature for Anchor Systems Documents anchor rod strength classes and internally threaded systems like HIS-N.