bolt vs screw
The difference between a bolt and a screw is one of those things that seems obvious until you try to define it. In fact, even hardware stores and engineers sometimes mix them up because they look so similar.
The easiest way to tell them apart isn't just how they look, but how they are installed and what they are holding together.
Here is the breakdown of the major differences:
1. How They Tighten (The Main Difference)
- Bolt: A bolt is designed to go through an unthreaded hole in two or more parts and is secured at the end using a nut. You typically turn the nut to tighten the joint, clamping the materials together in the middle.
- Screw: A screw cuts or mates with its own threads directly into the material (like wood, plastic, or sheet metal). It doesn’t use a nut; the material itself holds the screw in place.
2. The Shape and Threads
- Bolt: Usually has a flat, blunt tip (not pointy). The threads often don't go all the way to the head—there is usually a smooth section of the shank (called the grip length) designed to handle shear forces.
- Screw: Often has a sharp, pointed tip (especially wood and drywall screws) so it can pierce and cut into the material. The threads usually go all the way up to the head.
3. Tool Used
- Bolt: Usually tightened using a wrench (spanner) or socket because they have hexagonal (six-sided) heads.
- Screw: Usually tightened using a screwdriver or Allen key (hex wrench) because they have slots, Phillips (cross), or Torx (star) drives recessed into the head.
Comparison at a Glance
| Feature | Bolt | Screw |
|---|---|---|
| Needs a Nut? | Yes (usually) | No |
| Tip Shape | Flat / Blunt | Pointed / Tapered |
| Material Hole | Must be a clean, unthreaded through-hole | Can be a pilot hole, or no hole at all |
| Primary Tool | Wrench / Socket | Screwdriver / Hex key |
| Application | Heavy-duty, structural joints | Light to medium fastening (woodworking, electronics) |
The "Gray Area" Exception: > Sometimes you will see a "Machine Screw." It has a flat tip and fits into a pre-threaded metal hole (like inside an engine block or a camera tripod mount). Even though it looks like a small bolt and goes into a threaded hole, the industry still calls it a screw because it doesn't use a nut!