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EspañolExternally Threaded Fastener Used with a Nut
A bolt normally passes through unthreaded holes in the assembled parts and is secured with a nut. The bolt and nut work together to generate clamping force.
What Are Threaded Fasteners and How Do They Work
2026-07-13Fastener Knowledge Threaded Connection Guide
Mechanical Fastening and Assembly
What Are Threaded Fasteners and How Do They Create Reliable Assemblies?
Threaded fasteners are mechanical components that use matching internal or external threads to join two or more parts. They are widely used because they can generate controlled clamping force, support repeated assembly and provide a practical alternative to permanent joining methods.
The performance of a threaded fastener depends on more than its visible diameter. Thread pitch, thread form, material grade, engagement length, tightening torque, surface finish and load direction all affect connection reliability. A correctly specified threaded fastener can create a strong removable assembly, while an incorrectly selected fastener may loosen, strip, fracture or damage the connected parts.
Primary Function Create mechanical clamping force
Common Thread Location External, internal or both ends
Assembly Character Removable or adjustable connection
Key Selection Factors Diameter, pitch, length and grade
Technical File 01
What Are Threaded Fasteners?
Threaded fasteners are fastening components with a helical ridge formed around an external shaft or inside a hole. The helical profile allows one part to rotate into another while converting rotational movement into axial movement and clamping force.
A threaded fastener may be used with a matching nut, a tapped hole, an internally threaded insert or another threaded component. Bolts, screws, studs, threaded rods and some specialized anchors are common examples.
The term threads and fasteners covers both the geometry of the thread and the mechanical component carrying that thread. Thread compatibility is essential. Two components may appear similar in diameter but still be incompatible because of different pitches, thread angles or dimensional standards.
External Thread
A thread formed around the outside of a bolt, screw, stud or threaded rod.
Internal Thread
A thread formed inside a nut, tapped hole or threaded insert.
Thread Engagement
The axial length over which matching internal and external threads contact each other.
Technical File 02
What Do You Call a Threaded Fastener?
Fastener Driven into an Internal Thread or Material
A screw may enter a tapped hole or form its own mating thread in a suitable material. Screws are available with many head forms and drive styles.
Headless Fastener with External Threads
A stud is commonly threaded at both ends or along its entire length. One end may remain installed in a component while a nut secures the removable part.
Long Continuous Threaded Fastener
Threaded rod is used for supports, frames, suspended systems and assemblies requiring adjustable positioning over a longer distance.
Technical File 03
What Is an Example of a Threaded Fastener?
Hex Bolt
A general-purpose bolt with a hexagonal head, commonly tightened with a wrench and used with a nut or tapped hole.
Machinery frames, brackets, steel structures and equipment bases
Machine Screw
A smaller threaded fastener designed for accurately formed internal threads in metal, plastic or threaded inserts.
Electrical housings, instruments, covers and precision assemblies
Socket Head Screw
A compact fastener with an internal drive, suitable for applications where external wrench clearance is limited.
Machine tools, automation equipment, molds and mechanical modules
Double-End Stud
A headless threaded fastener with threads on both ends and an unthreaded or reduced section between them.
Engines, pumps, valves, flanges and removable equipment covers
Fully Threaded Stud
A cylindrical fastener threaded along its full length, allowing flexible nut placement and adjustable assembly thickness.
Pipe supports, structural connections and industrial suspension systems
Technical File 04
How Does a Threaded Fastener Create Clamping Force?
01
Rotational Input
A tool applies torque to the head, nut or drive feature of the threaded fastener.
02
Axial Movement
The helical thread converts rotation into linear movement along the fastener axis.
03
Joint Compression
The fastener head and nut, or the screw head and tapped component, compress the assembled parts together.
04
Fastener Tension
The fastener stretches elastically while the joined parts remain compressed, producing preload.
05
Load Resistance
The resulting preload helps resist joint separation, relative movement and vibration-induced loosening.
What Type of Assembly Can a Threaded Fastener Create?
A threaded fastener can create a removable, semi-permanent or adjustable mechanical assembly. The connection may be disassembled for inspection, repair or replacement without cutting or destroying the joined components.
Threaded connections can also create precision-adjustment assemblies, tensioning systems, structural joints, sealing joints and equipment mounting points.
Technical File 05
What Are Fasteners with Threads on Both Ends?
Studs and Double-End Studs
Fasteners with threads on both ends are generally called studs or double-end studs. They do not normally have a conventional bolt head. One threaded end may be installed permanently or semi-permanently in a tapped hole, while the opposite end receives a nut.
This arrangement is useful when the base component should not experience repeated thread wear. The stud remains in place while the nut is removed during maintenance.
Double-End Stud Threaded at both ends with an unthreaded center section
Tap-End Stud One end installs into a tapped component, while the other accepts a nut
Fully Threaded Stud Threaded continuously along the complete fastener length
Flange Stud Used to align and clamp pipe, valve and equipment flange connections
Technical File 06
What Is the Problem with Threaded Fasteners?
Threaded fasteners are reliable when properly selected and installed, but several recurring problems can reduce joint performance. These problems usually involve preload, thread condition, material compatibility or service loading.
Loosening
Vibration, joint movement, embedment of rough surfaces and insufficient preload can reduce clamping force over time.
Control MethodApply the correct tightening method and use an appropriate locking strategy where required.
Thread Stripping
Internal or external threads can shear when engagement length is insufficient or the mating material is too weak.
Control MethodIncrease engagement length, select a suitable material combination and avoid excessive torque.
Fastener Fracture
Excessive preload, overload, fatigue, hydrogen-related damage or stress concentration may cause the fastener to break.
Control MethodSelect an appropriate property class, control tightening and evaluate cyclic loading.
Cross-Threading
Misalignment during initial engagement can damage the first thread turns and prevent accurate tightening.
Control MethodBegin engagement by hand, maintain alignment and stop if abnormal resistance appears.
Corrosion
Moisture, chemicals, salt and incompatible metals can reduce the effective fastener cross-section or lock the threads.
Control MethodMatch the fastener material and coating to the operating environment.
Galling
Adhesive wear between mating threads can cause seizure, particularly in some metal combinations under high installation pressure.
Control MethodControl installation speed, surface condition, lubrication and material pairing.
Technical File 07
Threaded Fastener Failure Modes and Likely Causes
| Observed Condition | Possible Cause | Technical Effect | Inspection Focus |
|---|---|---|---|
| Nut rotates without tightening | Stripped internal or external threads | Required preload cannot be developed | Thread profile, material strength and engagement length |
| Fastener loosens after operation | Low preload, vibration or joint settlement | Joint movement and fatigue risk increase | Torque method, mating surfaces and locking arrangement |
| Bolt breaks near first engaged thread | Stress concentration, overload or fatigue | Complete loss of clamping force | Fracture surface, load history and fastener grade |
| Threads are damaged during assembly | Cross-threading, contamination or wrong pitch | Inaccurate torque and reduced engagement | Thread compatibility and installation alignment |
| Fastener cannot be removed | Corrosion, galling, deformation or excessive tightening | Maintenance time and component damage increase | Surface condition, environment and lubrication practice |
| Joined parts slide under load | Insufficient clamp force or smooth contact surfaces | Shear load transfers directly into the fastener body | Preload, friction condition and joint design |
Technical File 08
What Are Non Threaded Fasteners?
Non threaded fasteners do not rely on helical threads to produce attachment or clamping. They may use deformation, interference, spring force, a locking shape or a separate retaining feature.
The choice between threaded and non threaded fasteners depends on assembly speed, required removability, load direction, vibration, available space and production volume.
Rivets
Create a permanent or semi-permanent joint by deforming the rivet body.
Pins
Align parts, transmit shear loads or form pivots without a threaded connection.
Retaining Rings
Fit into grooves to prevent axial movement of components on shafts or inside bores.
Clips
Use spring force or formed geometry for fast installation and retention.
Keys
Fit between a shaft and hub to transmit torque and prevent relative rotation.
Press-Fit Components
Depend on dimensional interference between mating parts to maintain the connection.
Threaded Fastener Adjustable and generally removable
Non Threaded Fastener Often faster, compact or permanently retained
Selection Basis Load, service access, assembly rate and joint design
Technical File 09
What Measurements Are Needed to Specify Threaded Fastener Size?
A complete threaded fastener specification requires several measurements. Stating only the outside diameter is rarely sufficient because fasteners with the same diameter may have different pitches, lengths, head forms or mechanical properties.
Measurement What It Describes Why It Matters
Nominal Diameter
The basic external diameter used to identify the thread size.
Determines thread compatibility and contributes to tensile and shear capacity.
Thread Pitch
The axial distance between adjacent thread crests.
Distinguishes coarse, fine and specialized thread series.
Threads per Unit Length
The number of thread turns within a defined length.
Commonly used to identify some thread systems instead of direct pitch.
Fastener Length
The specified distance from the relevant head reference point to the end.
Must accommodate the joint thickness, washers, nut and required protrusion.
Threaded Length
The portion of the fastener containing usable external threads.
Affects nut placement and whether unthreaded shank passes through the shear plane.
Head Dimensions
Head width, height, diameter, bearing area and drive dimensions.
Determines tool access, seating area and available installation space.
Thread Engagement
The length of contact between the external and internal threads.
Influences stripping resistance and load distribution through the mating threads.
Grip Length
The total thickness of the materials clamped by the fastener.
Helps determine the correct fastener length and unthreaded shank position.
Technical File 10
Threaded Fastener Size Specification Example
Example Description M10 × 1.5 × 60
M10
Nominal thread diameter of 10 mm
1.5
Thread pitch of 1.5 mm
60
Nominal fastener length of 60 mm
A complete order or technical drawing may also state the head type, drive type, thread tolerance, material, mechanical property class, coating, washer arrangement and quantity.
Technical File 11
Coarse Threads and Fine Threads
Coarse Thread
Coarse threads have a larger pitch and fewer threads over the same axial distance. They are commonly selected for general assembly and materials where rapid installation and resistance to thread damage are important.
Assembly speed Faster axial movement per turn
Contamination tolerance Generally more tolerant of minor dirt and damage
Typical use General machinery and structural assemblies
Fine Thread
Fine threads have a smaller pitch and more threads within the same axial distance. They can provide finer adjustment and a larger tensile stress area for the same nominal diameter.
Adjustment Smaller axial movement per turn
Engagement More thread turns within a limited length
Typical use Precision equipment and controlled adjustment
Technical File 12
Material and Surface Treatment Selection
Carbon Steel
Suitable for a wide range of indoor machinery, frames and general mechanical connections.
Selection FocusMechanical grade, coating and operating humidity
Alloy Steel
Used where higher mechanical strength, fatigue performance or controlled heat treatment is required.
Selection FocusProperty class, hardness and service loading
Stainless Steel
Selected for humid, outdoor, hygienic or corrosive environments requiring improved corrosion resistance.
Selection FocusEnvironmental exposure and galling control
Brass or Copper Alloy
Used in electrical, decorative or specialized applications requiring conductivity or corrosion performance.
Selection FocusMaterial strength and mating-component compatibility
Common Surface Options Zinc plating, black finish, passivation, mechanical coating and application-specific protective finishes
Technical File 13
How to Select a Threaded Fastener for an Assembly
Stage A
Define the Joint
Identify the number of parts, total grip length, hole condition, required removability and available tool access.
Stage B
Define the Load
Determine whether the fastener will experience tension, shear, bending, vibration, fatigue or combined loading.
Stage C
Select the Thread
Choose the nominal diameter, pitch, thread form and engagement length according to the mating component and load requirement.
Stage D
Select the Material
Match the fastener strength and corrosion resistance to the connected materials and operating environment.
Stage E
Define Tightening Control
Establish the installation torque, lubrication condition, tightening sequence and inspection method.
Stage F
Confirm Service Access
Ensure the fastener can be installed, inspected and removed using the available space and maintenance tools.
Specification Support
What Information Helps Define a Suitable Threaded Fastener?
Clear application information helps determine the appropriate threaded fastener dimensions, material, mechanical grade, head form, drive type and surface treatment. A complete specification also reduces the risk of incompatible threads or insufficient engagement during assembly.
Fastener type Bolt, screw, stud or threaded rod
Thread specification Diameter, pitch and thread standard
Overall length Including required grip and engagement
Head and drive Selected according to tool access
Material grade Matched to strength and environment
Surface treatment Defined by corrosion and appearance needs
Technical File 14
Threaded Fasteners Frequently Asked Questions
What are threaded fasteners?
They are bolts, screws, studs, rods and related components that use internal or external threads to create a mechanical connection.
What do you call a threaded fastener without a head?
A headless threaded fastener is commonly called a stud or threaded rod, depending on its length, thread coverage and intended application.
Are fasteners with threads on both ends called bolts?
They are more commonly called double-end studs. A bolt normally has a formed head on one end.
Can a threaded fastener create a permanent assembly?
Threaded joints are normally removable, but corrosion, locking compounds, deformation or restricted access can make practical removal difficult.
Why do threaded fasteners loosen?
Common causes include insufficient preload, vibration, surface settlement, temperature change and relative movement between joined parts.
What measurements specify threaded fastener size?
The essential measurements include nominal diameter, pitch, length, threaded length, grip length, head dimensions and required thread engagement.
What are non threaded fasteners?
Rivets, pins, clips, retaining rings and keys are common non threaded fasteners that rely on deformation, interference or mechanical retention.
Can different thread pitches be assembled together?
No. Mating components must have compatible diameter, pitch, thread form and dimensional tolerance. Forcing mismatched threads can permanently damage both parts.
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