Bolt vs Screw: What's the Difference?
In everyday language “bolt” and “screw” are used loosely. In engineering, the distinction affects how the joint is designed and loaded. For recognizing head shape and drive type on the bench, see the visual reference (e.g. screw head types).
Definitions
A bolt is usually used with a nut; it passes through aligned, often unthreaded holes and the clamp load comes from tightening the nut. A screw typically engages a pre-tapped hole or a soft material and is tightened by the head; the thread carries the load into the material.
Comparison
| Bolt | Screw |
|---|---|
| Used with nut | Used in tapped hole or self-tapping |
| Through hole often unthreaded | Thread engages mating material |
| Load via tension in shank | Load via thread engagement |
| Hex head common | Various heads (slot, Phillips, hex, etc.) |
When to use which
Use bolts where you have two parts with aligned holes and want high clamp force with a nut. Use screws where one part is threaded or where you need to draw the fastener into the material (e.g. wood screws, machine screws into tapped holes). Thread sizes are the same—use our Thread Identifier or size chart to match.
FAQ
What is the difference between a bolt and a screw?
Bolts typically pass through unthreaded holes and use a nut; screws often engage a pre-tapped hole or form their own thread. Load direction and head design also differ.
Can I use a bolt without a nut?
Only if the hole is threaded (then it acts like a screw). In unthreaded holes, the nut (or threaded counterpart) is required for the joint.
Do bolts and screws use the same thread sizes?
Yes. Metric and imperial thread sizes (e.g. M6, 1/4-20) apply to both. Use our screw size chart or converters to match sizes.
Related
Tools: Thread Identifier, Metric to Imperial Converter
Charts: Universal Screw & Bolt Size Chart, Screw Size Chart
Guide: Thread Types Explained