Bolt vs. Screw: Which Fastener for Your Project
A bolt clamps with a nut and needs both sides; a screw cuts its own thread and needs one side. Access, load, and whether the joint ever reopens — that decision takes ten seconds once you know the split.
| Feature | Hex Bolt | Wood Screw |
|---|---|---|
| Tightened by | Turning the nut | Turning the head |
| Needs a nut? | Yes — or a tapped hole | No — threads into the material itself |
| Hole type | Clearance hole through both parts | Pilot hole, or self-tapping |
| Access needed | Both sides of the joint | Head side only |
| Shear strength | High — smooth shank spans the joint | Moderate — threads weaken the shear plane |
| Disassembly | Unlimited — the nut takes the wear | Limited — threads strip the substrate |
| Install speed | Slow — nut, washers, two tools | Fast — one driver, seconds each |
| Best for | Steel, machinery, anything structural | Wood, sheet metal, drywall, one-sided joints |
Verdict
FAQ
Can I use a screw instead of a bolt?
In non-structural work — wood framing, sheet metal, plastic — often yes. In structural, code-governed, or safety-critical joints, no: codes like AISC 360 require bolts with verifiable preload.
What is the ASME definition of bolt vs. screw?
ASME B18.2.1 draws the line at assembly: a bolt is tightened by turning a nut, a screw by turning its head. A hex cap screw driven into a tapped hole is technically a screw; the same part with a nut is a bolt.
Is a lag screw a bolt or a screw?
A screw — it threads directly into wood with no nut. Lag bolt is the same part under its nickname, which is why the name confuses everyone.
Why do structural joints require bolts?
Preload can be set precisely with a torque wrench, verified by inspection, and re-checked years later — and the replaceable nut takes thread wear instead of the structure. Screws offer none of that.