The Base Material Picks the Anchor
Anchor selection is one of the few decisions on a job where the wall decides for you. Drill into solid concrete and you have a different set of options than you do in hollow block, and both differ again from drywall with nothing behind it. Start with what you are drilling into, then work out to load and length.
Solid Concrete, Block, and Brick
Poured concrete is the friendliest base material because it is solid all the way through, so an anchor can develop its full holding strength anywhere you drill. Hollow block is not: the face shell is thin and the cell behind it is empty, so an anchor set in the middle of a block face has far less to grip than one set in the mortar joint or a filled cell. Brick behaves somewhere between the two depending on whether it is solid or cored. When you cannot tell what is behind the surface, drill a test hole before committing to an anchor type across a whole run of fasteners.
Concrete Screw Anchors
A concrete screw anchor threads directly into a drilled hole with no expansion sleeve, shield, or setting tool involved. Cutting its own threads into the masonry is what makes it fast, and it is also removable, which matters on temporary supports and on anything likely to be relocated. Two head styles cover most electrical work. Slotted hex washer head drives with a nut driver and leaves a broad bearing surface, which suits straps, standoffs, and anything with a slotted or oversized hole. Phillips flat head countersinks flush, so it is the choice where the fastener head cannot sit proud of the surface.
The critical variable is embedment, meaning how deep the threads actually engage the masonry, not the total screw length. A longer screw holding a thicker fixture may end up with less material engaged than a shorter one through a thin strap. Match the length to the fixture thickness plus the embedment the manufacturer specifies, and drill the hole deeper than the screw so dust has somewhere to go.
Ribbed Plastic Anchors for Light Loads
Ribbed tubular plastic anchors are the small white, green, and blue anchors sized by screw gauge, and they work by expanding against the sides of a drilled hole as the screw goes in. They are inexpensive and quick, and within their intended range they are perfectly reliable for light static loads like a cover plate, a small strap, or a low-voltage device. They are not a substitute for a masonry anchor under real load, and they perform poorly in soft or crumbling substrate where there is nothing firm for the ribs to bite into. Match the anchor color and size to the screw gauge printed on the packaging rather than eyeballing it.
Understanding Load: Shear, Pullout, and Safety Factor
Anchor ratings come in two directions and they are not interchangeable. Shear is the load acting across the anchor, which is what a conduit strap on a wall mostly sees. Pullout, or tension, is the load trying to pull the anchor straight out of the material, which is what an overhead support carries. An anchor can be strong in one and weak in the other. Published values also assume sound base material, correct hole size, and full embedment, so apply the manufacturer's safety factor rather than designing to the raw number. For anything overhead or life-safety related, the engineer of record sets the requirement, not a rule of thumb.
Drilling the Hole Correctly
Most anchor failures trace back to the hole, not the anchor. Use the bit diameter the anchor specifies, because a hole even slightly oversized cuts holding power sharply and an undersized hole can crack the anchor or the masonry during installation. Drill deeper than the anchor needs so debris has somewhere to fall, then clear the dust out before setting anything, since packed dust prevents full seating. Keep the drill perpendicular to the surface; an angled hole loads the anchor unevenly and reduces what it can hold.
Spacing and Edge Distance
Two anchors set close together in concrete can pull out a single cone of material between them and fail as a pair, even though each would have held alone. The same applies near an edge, where there is not enough surrounding material to develop full strength. Manufacturers publish minimum spacing and edge distance for exactly this reason, and both scale with anchor diameter and embedment depth. On a run of fasteners, plan the layout before drilling rather than discovering the conflict at the last hole.
What the Anchor Is Holding
An anchor is only half of a fastening. The screw or bolt that goes through it has to match the anchor's diameter and the fixture's hole, and Lumera's screws and bolts collection covers those.
For conduit runs and cable bundles that need to be carried along a wall or ceiling rather than pinned at a single point, the straps and supports collection has the hardware that mounts on top of the anchor.
Where cable is being bundled or tied off rather than clamped, cable ties and tie wire handle that part of the run.
Enclosures mounted to masonry are one of the most common uses for these anchors, and the device and outlet boxes collection covers the boxes that get fastened up.
To see the full fastening range in one place, including hardware not listed on this page, browse fasteners and hardware.
Common Questions About Anchors
Which anchor should I use in concrete?
A concrete screw anchor is the most common choice for electrical work because it threads directly into a drilled hole, needs no expansion sleeve or setting tool, and can be removed later. Match the diameter and length to the fixture thickness plus the embedment depth the manufacturer specifies.
Do plastic anchors work in concrete or block?
Ribbed plastic anchors will hold light static loads in sound masonry, but they are not a substitute for a proper concrete anchor under real load. They also perform poorly in soft or crumbling material where the ribs have nothing firm to grip. For anything carrying weight, use a masonry-rated anchor instead.
What is the difference between shear and pullout strength?
Shear is the load acting across the anchor, which is what a wall-mounted strap mostly experiences. Pullout, or tension, is the load pulling the anchor straight out of the material, which is what an overhead support carries. An anchor can be rated well in one direction and poorly in the other, so check the value that matches your application.
What size hole do I drill for an anchor?
Use the exact bit diameter the anchor specifies. An oversized hole cuts holding power sharply, and an undersized one can crack the anchor or the base material. Drill deeper than the anchor requires so debris has room to fall, then clear the dust before setting the anchor.
How far apart do anchors need to be in concrete?
Anchors set too close together can pull out a shared cone of material and fail as a group even though each would hold on its own. The same applies too near an edge. Manufacturers publish minimum spacing and edge distances that scale with anchor diameter and embedment depth, so lay out the pattern before drilling.
Can concrete screw anchors be reused?
They can be removed, which is one of their advantages, but reusing the same anchor in the same hole gives up holding strength because the threads it originally cut are no longer a tight match. For a permanent installation, set a new anchor in a fresh hole.
