Through bolt, sleeve anchor or shield anchor — what is the difference?
Three heavy masonry anchors that look similar and set differently — how each grips, which suits a through-hole and which does not, and where none of them belongs.
- Difficulty
- intermediate
- Time
- 15 min
- Read
- 3 min
Short answer
A through bolt is a stud with a wedge clip at the end that drives through the item into the wall and expands at the tip. A sleeve anchor expands along a longer sleeve, so it suits weaker material and slightly oversize holes. A shield anchor sets first and then takes a separate bolt, so the item can be removed and refitted. All three exert outward pressure and none belongs near an edge or in weak material.
Once a fixing has to hold something genuinely heavy in masonry — a gate post, a heavy bracket, machinery, a balustrade base plate — nylon plugs are out and you are choosing between three families of steel anchor. They install differently and that difference usually decides which one the job allows.
Step by step
- Through bolt: use where you can drill through the item into the wall.A threaded stud with a tapered end and a split wedge clip. You drill through the fixture and wall in one pass, tap the whole assembly in, and tighten the nut — which pulls the taper into the clip and wedges it against the hole at the deep end.
- Understand the through bolt's limitation.It expands at a single point at the tip, so it needs sound dense material and full embedment. In soft or crumbly brick it can crush a small pocket and go loose.
- Sleeve anchor: use in less-than-perfect masonry.The expanding element is a longer sleeve, so the outward force is spread over a greater length of hole. That makes it more tolerant of weaker material and of a hole that is not perfect, and it is what many people mean when they say expansion bolt.
- Shield anchor: use where the item must come off again.The shield is set into the hole and expanded on its own, leaving a threaded socket. The fixture is then bolted to it, and can be unbolted and refitted repeatedly without disturbing the anchor. This is the one for machinery feet, removable posts and anything serviced.
- Match the setting method to what you can drill.Through bolts and sleeve anchors need a hole through the item that lines up perfectly, which is easy if you can drill both together and awkward if the item is already made. A shield anchor is set first and then located, which suits a fixture with existing holes.
- Respect edge distance and spacing for all three.They all work by pressing outwards, and that is the load that splits a brick or a slab edge. If you cannot get the distance, the answer is a resin anchor, not a smaller expansion anchor.
- Use none of them in weak or hollow material.Aerated block, perforated brick, soft lime-mortared brick, old rendered rubble. Expansion in weak material is a crushing action, not a gripping one.
- Tighten to the maker's torque, then stop.These anchors set by tension. Under-tightening leaves them unset; over-tightening crushes the masonry around the expansion point and the anchor goes slack, which feels exactly like under-tightening.
Tips
- Hexagon-headed through bolts leave a nut and thread proud. Countersunk and internally threaded types exist where the finish matters.
- A through bolt cannot usually be removed cleanly — the wedge stays in the hole. If you may need to remove it, either plan to cut it flush or use a shield anchor.
- All three come in stainless as well as zinc-plated steel. For anything outdoors or in a wet plant room, specify the stainless version from the start.
Common mistakes
- Using an expansion anchor near the edge of a brick or slab — The outward force is precisely the load an edge cannot take, and it splits a lens off the face. Use resin where the distance is not available.
- Tightening a through bolt until it stops turning — Past the setting torque you are crushing the masonry rather than tensioning the anchor, and the fixing ends up loose in an enlarged pocket.
Questions people ask
Which is strongest?
In sound dense concrete, all three can be very strong and the published figure for the specific product matters far more than the family. In imperfect masonry, a sleeve anchor or a resin anchor is generally more forgiving than a through bolt.
When should I use resin instead?
Close to an edge, in soft or old brick, in perforated brick, in stone, where the hole has come out oversize, or where you need the highest capacity available in a given depth.