BRICK WALL MASONRY CONCRETE ANCHORS THROUGHBOLT LONG THREADED EXPANSION BOLTS

A standard expansion anchor (such as a sleeve anchor or wedge anchor) is installed into a blind hole drilled into one material only — the anchor expands inside that single substrate. A throughbolt passes completely through both the fixture and the substrate, with the expansion sleeve gripping the back face of the material. This through-fixing method is often stronger in tension because the load is distributed across the full thickness of the substrate rather than relying solely on the drilled hole depth.

Start with the load requirement: M6 suits lighter brackets and cable management fixings; M8 and M10 are appropriate for medium structural loads such as railing posts and machinery bases; M12 handles heavy-duty structural connections. For length, add the thickness of the fixture (the item being bolted) to the thickness of the substrate (the wall or slab), then select the next available length that comfortably spans both. Leave enough thread protruding to fit a washer and nut with at least 3–4 full thread engagements.

The required clearance hole diameter is specified in each variant name. M6 bolts require a 10 mm hole, M8 requires 12 mm, M10 requires 14 mm, and M12 requires 16 mm. Drill through both the fixture and the substrate using a hammer drill and masonry bit of the correct diameter. A hole that is too small will prevent the bolt from passing through; a hole that is too large will reduce the clamping area of the expansion sleeve.

Corrosion resistance depends on the material and surface finish of the specific bolt. For outdoor, coastal, or permanently damp environments, select a variant with a corrosion-resistant finish or material. If you are unsure which finish is appropriate for your exposure class, contact us to confirm before ordering. Using an uncoated carbon steel bolt in a wet environment without protection will lead to rust staining and eventual fastener degradation.

Throughbolt expansion anchors rely on solid substrate contact to develop their holding strength. Hollow-core concrete block, aerated autoclaved concrete (AAC / Hebel), and lightweight cellular block do not provide the continuous bearing surface needed for the expansion sleeve to grip reliably. For these substrates, use a chemical anchor system with a suitable resin and a threaded rod instead. Contact us if you need guidance on the correct anchor type for your substrate.

Most standard railing post base plates use 4 fixing points, so a pack of 5 gives you one spare per post. For a run of 10 posts you would need 40 bolts — a combination of packs of 25 and 10 or 20 is typically the most economical. For structural brackets, always follow the engineer's specification for the number and size of fixings required. When in doubt, order a small quantity first to verify fit and installation before committing to a full project quantity.

Recommended installation torque varies by thread diameter and substrate type. As a conservative starting point for solid concrete: M6 typically 10–15 Nm, M8 typically 20–30 Nm, M10 typically 40–55 Nm, M12 typically 60–80 Nm. Always tighten gradually and evenly. Over-tightening can strip the thread or crack brittle substrates such as old brick. For load-critical applications, contact us to confirm the manufacturer's specified installation torque for the exact variant you are using.