A Thunderbolt is a self-tapping masonry anchor — you'll also see them sold as concrete bolts or masonry screws. Unlike a sleeve anchor or a through bolt, a Thunderbolt doesn't expand. Its hardened thread cuts into the base material itself, so there's no wall plug, no resin and no outward pressure on the concrete, brick or block.
That single difference drives everything that makes Thunderbolts popular: you can install one in seconds with an impact driver, fix close to edges and closer together than expansion anchors allow, and unscrew the fixing cleanly when the job is temporary or needs repositioning.
One terminology trap to clear up first: "thunderbolt" started as a brand name (Ramset/Reid's Thunderbolt™) but has become a generic trade term in the UK. When someone asks for "a thunderbolt", they almost always mean any self-tapping masonry anchor of this type.
How to install a Thunderbolt
- Drill a hole the same diameter as the anchor, slightly deeper than you need — the extra depth gives dust somewhere to go.
- Clean the dust out of the hole. A blow-out pump or a quick blast of air is enough for most jobs.
- Drive the Thunderbolt in with an impact driver, using light pressure until the thread bites.
- Tighten to pull the fixture down. To remove or reposition the fixing, simply unscrew it — the hole can usually take a re-drive.
No wall plug, no resin, no torque wrench — the concrete, brick or block becomes the thread.
Where Thunderbolts work best
- Materials: concrete, solid brick, concrete block and stone.
- Close-to-edge fixing: no expansion pressure means less risk of splitting or blowing the substrate near edges and corners.
- Temporary or removable work: unscrews cleanly — temporary hoarding, framing, jig and plant fixing.
- Fast installs: frames, brackets, battens, conduit clips, shelving, gating — anywhere speed matters.
When NOT to use a Thunderbolt
This is the section most supplier pages skip — and it's where most failed fixings come from.
- Weak or low-strength brick, hollow block and mortar joints: holding power depends on embedment depth and the strength of the base material. Always do a test fix before you commit the job.
- Cracked concrete and seismic or fire-rated applications: these need an anchor with certified performance data (ETA-rated products). A Thunderbolt's unpublished holding values can't be substituted for them.
- Heavy structural loads in concrete: where the fix can sit away from an edge, an expansion anchor (sleeve anchor or through bolt) with published load tables is usually the better engineering choice.
- Over-torquing: the thread cuts as it turns — excessive power or speed can strip the thread, especially in softer brick. Let the driver do the work.
Thunderbolt vs sleeve anchor vs through bolt
| Thunderbolt | Sleeve anchor | Through bolt | |
|---|---|---|---|
| How it grips | Thread cuts into the material | Sleeve expands when torqued | Cone expands against the hole wall |
| Pressure on the material | None — safe near edges | High | High |
| Close-to-edge fixing | Good | Poor | Poor |
| Removable & reusable | Yes — unscrews cleanly | Difficult | Difficult |
| Base materials | Concrete, brick, block, stone | Concrete, brick, block | Concrete only |
| Best for | Fast, removable, near-edge masonry fixings | General heavy-duty fixing | Heavy structural concrete |
Choosing the right size
Thunderbolts are sized by diameter (M5 to M16) and length (30–200mm at Fastco). As a rule of thumb: the thicker the diameter, the greater the holding power; the deeper the embedment, the better the grip — so choose a length that gives you a sound embedment depth in the base material after passing through the fixture. Heads come in hexagon, hexagon flange and countersunk Torx 25; most sizes are zinc-yellow plated, with galvanised M16 for coastal, marine and other corrosive environments.
Note on drill sizes: match the drill bit to the anchor diameter and drill slightly deeper than the embedment. We're preparing a size-by-size drill and hole-depth table for this post once we've verified the figures against the official data sheet — we won't publish numbers we haven't checked.
Frequently asked questions
Do Thunderbolts need wall plugs?
No — the anchor cuts its own thread into the base material, so no plug or resin is needed.
What size drill bit do I need?
The same diameter as the anchor, drilled slightly deeper than the embedment depth.
Can Thunderbolts be removed and reused?
Yes — unscrew them with the same driver. Ideal for temporary works and repositioned fixtures.
Can you use Thunderbolts in brick and block?
Yes — solid brick, block and stone as well as concrete. Take care in hollow block and weak brick, where holding power depends on the base material.
Thunderbolt or sleeve anchor?
Near an edge, or need to remove it later? Thunderbolt. Heavy load where the fix can sit away from edges? A sleeve or through bolt may carry more.
Shop Thunderbolts at Fastco
Fastco stocks Thunderbolts from M5 to M16, 30–200mm long, in hexagon, hexagon flange and countersunk Torx 25 heads. Browse the full Thunderbolt range, with trade packs and bulk discounts and fast UK delivery. Not sure on substrate or size? Call 01270 252326 — over 25 years of fixing experience, on the phone, no charge.
