What is the difference between a bolt and a screw?

Short Answer:

The difference between a bolt and a screw lies mainly in how they are used and how they grip materials. A bolt is usually used with a nut and passes through a hole in two or more parts, while a screw is used without a nut and directly threads into the material it fastens. Bolts provide clamping force through the nut, while screws create the holding force by their own threads.

Bolts are generally used for joining machine parts with nuts and washers, while screws are used for fastening into softer materials like wood, plastic, or tapped holes in metal. Understanding the difference helps in selecting the right fastener for strength, reusability, and reliability in any application.

Detailed Explanation:

Difference between a bolt and a screw

In mechanical engineering and everyday construction, fasteners play a key role in joining components securely. Two of the most common fasteners are bolts and screws. Although they may look similar, they work differently and are used in different situations. Knowing the exact difference helps in choosing the right fastener for any job, whether in machines, furniture, structures, or household fittings.

Let’s understand in detail how a bolt differs from a screw, based on usage, design, installation, and strength.

What is a bolt?

A bolt is a threaded fastener that is always used with a nut. It is inserted into a pre-drilled hole in the components being joined, and a nut is tightened on the opposite side to clamp the parts together.

Key features:

  • Requires a nut to work
  • Tightened using a spanner or wrench
  • Provides strong and reusable joints
  • Commonly used with washers for even load distribution

Example:
A hex bolt used with a hex nut and washer in joining two metal plates.

What is a screw?

A screw is a self-threading fastener that is screwed directly into a material. It creates its own mating thread when turned, especially in softer materials like wood, plastic, or when inserted into a tapped (threaded) hole in metal.

Key features:

  • Does not need a nut
  • Holds by engaging its threads in the base material
  • Tightened using a screwdriver, Allen key, or wrench
  • Often has pointed tips for easy entry into the material

Example:
A wood screw used to join two wooden boards.

Major differences between bolt and screw

  1. Use of nut
  • Bolt: Always used with a nut or tapped hole
  • Screw: Does not need a nut; threads directly into material
  1. Type of fastening
  • Bolt: Clamp-type fastening; used to hold two parts together with pressure
  • Screw: Threaded fastening; holds by its thread in one part
  1. Installation method
  • Bolt: Inserted through hole and nut is tightened
  • Screw: Rotated directly into material or pre-threaded hole
  1. Load handling
  • Bolt: Stronger and more suitable for high-load applications
  • Screw: Used in lighter-duty or non-critical connections
  1. Tools used
  • Bolt: Tightened with wrenches or spanners
  • Screw: Tightened with screwdrivers, hex keys, or torque drivers

Applications of bolts

  • Machine joints
  • Engine parts
  • Bridges and steel structures
  • Automotive assembly
  • Heavy-duty frames

Bolts are selected when strength, reusability, and safety are important.

Applications of screws

  • Woodworking
  • Plastic assembly
  • Tapped holes in machines
  • Appliances and electronics
  • Furniture assembly

Screws are chosen for simplicity, low cost, and faster assembly.

Which is better – bolt or screw?

It depends on:

  • Load requirement: Bolts for heavy load, screws for light to medium
  • Reusability: Bolts are better if the joint is to be opened and reused often
  • Assembly time: Screws are faster for one-side access
  • Precision: Screws offer better control in tight spaces

Both bolts and screws are essential, and engineers select them based on design need, strength, and ease of use.

Conclusion

Bolts and screws are both widely used fasteners but differ in function, design, and application. A bolt is used with a nut to clamp components, while a screw threads directly into the material. Bolts are stronger and used in machines and structures, whereas screws are easy to use and common in wood, plastic, and electronics. Understanding their difference helps in choosing the right fastener for safe, efficient, and long-lasting joints.