They're both steel masonry anchors that go into a drilled hole with a hex head and a torque wrench or impact driver — and on a shelf they look like close cousins. But they hold in completely different ways, they're approved for completely different jobs, and one of them will fail a specification the other sails through.
The short version: a Thunderbolt cuts its own thread and doesn't expand; a through bolt expands to grip. Everything else — materials, loads, edge distance, reusability — flows from that one difference.
Quick reference — Thunderbolt vs through bolt
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|
Thunderbolt |
Through bolt |
|---|---|---|
|
How it holds |
Hardened thread cuts into the base material — no expansion |
Torque-controlled expander cone wedges the sleeve against the hole wall |
|
Materials |
Concrete, stone, brick, block |
Concrete only — not brick, block or general masonry |
|
Sizes we stock |
5, 6, 8, 10, 12 and 16mm |
M6–M24, full catalogue |
|
Certification |
General-purpose; no published ETA load data |
CE marked, ETA Option 7 for non-cracked concrete |
|
Edge & spacing |
Can fix close to edges and close together |
Expansion pressure needs edge distance and spacing |
|
Removal |
Unscrews cleanly — re-drive often possible |
Can be backed out, but grip is degraded after removal |
|
Speed |
Fastest — drill, blow out, drive |
Fast, but torque-controlled and hole-tolerance matters |
How each one actually holds
A Thunderbolt is a self-tapping masonry anchor — you'll also see it sold as a concrete bolt or masonry screw. Its hardened thread cuts into the substrate as you drive it, so the base material itself becomes the nut. There's no wall plug, no resin and no outward pressure on the hole. That's why a Thunderbolt can sit close to an edge and close to its neighbours: it isn't pushing the material apart.
A through bolt (also called a wedge anchor or expansion anchor) is the opposite philosophy. You drill a hole to tolerance, hammer the anchor through the fixture, and as you torque the nut the taper at the bottom pulls an expander clip outward, wedging it hard against the hole wall. That expansion is where the grip — and the higher certified loads — come from. It's also why a through bolt needs edge distance: the expansion stress has nowhere to go near a corner or a thin section.
Where the Thunderbolt wins
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Mixed materials. It's the one anchor that behaves in concrete, solid brick, concrete block and stone. If the job moves between substrates — a frame bolted through brick into block, say — one fixing covers it.
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Speed. Drill, blow the dust out, drive. No torque control, no depth gauge precision. For brackets, battens, conduit clips, gating and shelving, it's the fastest masonry fixing on the van.
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Temporary or repositionable work. Unscrew it and the hole will usually take a re-drive. Ideal for hoarding, jigs and plant fixing.
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Close to edges. No expansion pressure means far less risk of splitting brickwork or blowing a corner out.
Where the through bolt wins
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Specified structural work in concrete. Our through bolts are CE approved with an ETA Option 7 assessment for non-cracked concrete. When a drawing calls for a certified anchor with published load data, this is the fixing that ticks the box — a Thunderbolt's holding values aren't published, so it can't be substituted on a spec.
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Heavier loads. The expansion grip delivers higher working loads than a cut thread in the same concrete, and the range runs to M24 where Thunderbolts stop at 16mm.
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Permanent plant and machinery fixing. Once set and torqued, an expansion anchor is the standard answer for equipment that isn't meant to move.
The most common mix-up we hear: through bolts get specified for brickwork because they look like a "bigger" anchor. They're not rated for it — through bolts are concrete-only. In brick or block, use a Thunderbolt, a shield anchor or a sleeve anchor instead.
Choosing in ten seconds
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Concrete and a spec or heavy load? Through bolt.
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Brick, block or stone — or you're not sure what you'll hit? Thunderbolt.
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Temporary fix, or going in near an edge? Thunderbolt.
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Drawing says "ETA-approved expansion anchor"? Through bolt — and keep the product information sheet for the file.
Whichever you pick, drill the hole the diameter of the anchor, go slightly deeper than the embedment, and blow the dust out — it's the cheapest ten seconds in fixing and the difference between a fixing that holds and one that spins.
Planning a concrete or masonry job? Browse Thunderbolts and through bolts — trade prices, stock in Crewe and fast UK delivery. Questions on a specific fixing? Call the team on 01270 252 326.
Further reading: What is a Thunderbolt anchor? (deeper on install technique and the "when not to use" cases) · Product Information: Through Bolts · Product Information: Thunderbolts · Plasterboard fixings explained if your job is internal rather than masonry.
