The Ultimate Guide to Fastener Classification: From Threaded to Non-Threaded, Mastering 10 Key Types and Their Applications

Introduction: A World of Precision Beyond “Screws and Nuts”

When people talk about “fasteners,” ordinary screws and nuts often come to mind first. However, this industry is far more precise and systematic than you might imagine. From the steel structures of skyscrapers to the internal chips of smartphones, vastly different applications demand vastly different connection technologies. Choosing the wrong type of fastener can lead to joint failure, increased costs, or even safety hazards.

Therefore, a systematic understanding of fastener classification is not only a professional requirement for engineers and procurement specialists but also the foundation for ensuring the success of any project. This article will take you deep into the world of fasteners, moving beyond the simple concept of a “screw” to explore the ten core classification systems based on function, structure, and application.

Body: A Deep Dive into 10 Core Fastener Classifications

Fasteners can be primarily classified based on whether they are threaded, removable after installation, and their specific locking or load-bearing mechanisms. The following are the ten core categories based on industry consensus:

1. Bolts

A bolt is a rod-shaped fastener with external threads, typically used in conjunction with a nut. It passes through two or more components with clearance holes, generating clamping force by tightening the nut.

Key Characteristics: Generally used in pairs with a nut; various head shapes (hex, round, countersunk); shank can be fully or partially threaded.

Common Types: Hex bolts, carriage bolts, anchor bolts, high-strength structural bolts (e.g., ASTM A325).

Typical Applications: Steel structure connections, heavy machinery assembly, bridge construction.

2. Screws

A screw is a fastener that is directly driven into a pre-tapped threaded hole (internal threads) in the mating material, without the need for a nut. It generates clamping force by engaging its threads with the base material.

Key Characteristics: Typically used alone; head has a drive recess (Phillips, slotted, hex socket, etc.); fully threaded shank.

Common Types: Machine screws, self-tapping screws (for plastics, thin metal), wood screws, thread-forming screws.

Typical Applications: Appliance housing assembly, furniture making, automotive interior trim fastening.

3. Studs

A stud is a headless, rod-shaped fastener with threads on both ends or along its entire length. One end is often permanently screwed into a component (e.g., an engine block), while the other end is used to mount another part secured with a nut.

Key Characteristics: Double-ended threading; ideal for applications where one of the joined parts needs frequent disassembly.

Common Types: Double-end studs, weld studs.

Typical Applications: Engine cylinder head installation, flanged pipe connections, large mold fixing.

4. Nuts

A nut is an internally threaded fastener used in conjunction with a bolt or stud, providing clamping force through rotation. It is a key component of removable connections.

Key Characteristics: Internal threads; various shapes to accommodate different tools and locking needs.

Common Types: Hex nuts, nylon insert lock nuts, acorn nuts, flange nuts.

Typical Applications: Used with bolts in nearly all removable mechanical joints.

5. Washers

A washer is a thin plate placed under a nut, bolt head, or screw head and the joined part. Its primary functions are to distribute pressure, prevent surface damage, provide sealing, or assist in locking.

Key Characteristics: Usually a flat ring; diverse materials (metal, rubber, plastic).

Common Types: Plain washers, spring washers (lock washers), serrated lock washers, sealing washers.

Typical Applications: Protecting soft material surfaces, preventing nut loosening from vibration, pipe sealing.

6. Rivets

Rivets are permanent mechanical fasteners. During installation, one end (the tail) is deformed and expanded by hammering or hydraulics, thereby clamping the components together. They are not removable after installation (except by destruction).

Key Characteristics: Permanent connection; requires special tools for installation; excellent shear strength.

Common Types: Solid rivets, blind rivets (pop rivets), drive rivets.

Typical Applications: Aircraft skin, steel bridge structures, canvas backpacks, denim jeans hardware.

7. Pins

A pin is a non-threaded rod-shaped fastener that primarily relies on interference fit or shear force to fix the position of parts, transmit loads, or act as a safety device.

Key Characteristics: Usually smooth cylindrical or tapered; simple installation.

Common Types: Dowel pins, taper pins, cotter pins, spring pins (roll pins).

Typical Applications: Locating gears on shafts, hinge connections, safety pins (for overload prevention).

8. Retaining Rings / Circlips

A retaining ring is an elastic metal ring installed in a groove on a shaft or in a bore. It limits the axial movement of a part while allowing rotation.

Key Characteristics: Snaps into pre-machined grooves; easy to install and remove; space-saving.

Common Types: Internal retaining rings, external retaining rings, E-rings.

Typical Applications: Axial fixation of bearings on shafts, gear positioning, piston pin retention.

9. Fastener-Washer Assemblies

These products combine a screw or bolt with a washer possessing a specific function (e.g., locking, sealing) pre-assembled, improving assembly efficiency and ensuring consistent performance.

Key Characteristics: Integrated design; reduces part count; reliable performance.

Common Types: Screws with washers attached, weld bolt and washer assemblies, screw and pre-assembled lock washer units.

Typical Applications: Automotive assembly lines, mass production of appliances, applications requiring high-reliability locking.

10. Specialty Fasteners

Non-standard or high-performance fasteners designed to meet the needs of specific industries or extreme environments.

Key Characteristics: Special materials, design, or processing; meets specific physical or chemical performance requirements.