Connector, Coupling, Connection and Long hexagon, Square and Round Nuts

Connector Nuts – Technical Overview and Custom Manufacturing

Trojan Special Fasteners Ltd manufactures connector nuts to exact customer specifications, including a wide range of sizes, lengths, thread types and material/finish combinations.

What Are Connector Nuts?

Connector nuts are also called coupling nuts, joining nuts, long nuts, extension nuts, and studding connectors. These elongated internally threaded fasteners are used to join two male threaded components, such as all-thread rods or studs.

Available in hex, double-flat or round profiles
Used in construction, rail, electrical and plumbing
Connects two rods, aligns components, or adds length
Can combine different thread types or directions
Often used in adjustable or tensioned assemblies

Standard Threading Options

We machine threads to match your design intent using recognised international thread forms:

ISO Metric (e.g. M10 × 1.5)
UNC / UNF Inch (e.g. ½″–13 UNC)
BSW / BSF (British Standard)
BSPP or BSPT for pipe-threaded couplings
Custom threads – trapezoidal, acme, etc.

Connector nuts can feature same-size threads both ends, or be reducing nuts with mixed diameters or pitches. Left-hand/right-hand configurations are common in turnbuckle assemblies.

Length and Engagement Best Practices

Standard engagement is 1 × nominal diameter per side
Heavier-duty uses may require 1.5× or 2× engagement
Total nut length depends on application strength needs

Example: A connector nut for M12 should be at least 24mm long (12mm thread per side).

Hex Size Dimensions (Metric Standard)

Thread M6 - Across Flats (A/F) 10 mm
Thread M8 - Across Flats (A/F) 13 mm
Thread M10 - Across Flats (A/F) 17 mm
Thread M12 - Across Flats (A/F) 19 mm
Thread M16 - Across Flats (A/F) 24 mm
Thread M20 - Across Flats (A/F) 30 mm
Thread M24 - Across Flats (A/F) 36 mm

Custom flats, non-hexagonal shapes, or smooth cylindrical profiles are available on request.

Material Options and Mechanical Grades

We manufacture connector nuts from bar using CNC turning and tapping:

Steel grades – EN1A, EN8
Stainless steels – 303, 304, 316
Brass – electrical or decorative use
Aluminium – lightweight, corrosion-resistant

We can meet mechanical performance standards such as:

Class 8, 10 or 12 steel (to ISO 898)
B1083 and BS1768 for inch fasteners
316 stainless for marine-grade service

Available Surface Treatments

Bright zinc plating (BZP)
Zinc flake plating (such as Geomet or KL100)
Nickel plating
Black oxide
Phosphate coating
Passivation for stainless steel

These help resist corrosion, improve conductivity, or enhance aesthetic finish.

Precision and Tolerances

Internal threads cut or formed to:

ISO 6H (standard fit) or ISO 4H/5H (tight fit)
UN 2B (inch) or UN 3B (tight tolerance)

We maintain strict tolerances on:

Thread concentricity
Outer dimensions
Overall length

Optional Features and Enhancements

Left/right-hand thread combinations
Mixed thread forms or diameters
Laser-etched part identification
Sight holes to confirm thread engagement
Thread-locking patches
Weldable base ends or anti-rotation flats
Precision OD grinding for tight tolerance inserts

Applications of Connector Nuts

Suspension systems
Scaffolding and formwork
Rail, tram and transport fixings
Pipe brackets and strut channel systems
Adjustable jigs, fixtures and tooling
Architectural and decorative installations

Design Considerations

Use thread locking where vibration is present
Check alignment of threads to avoid cross-threading
Use torque settings appropriate to material strength
Avoid over-tightening thin-walled couplers

What are common problems with connector nuts and how can they be prevented?

One of the main problems associated with connector nuts is that they can vibrate loose over time if not properly tightened. This can be a serious issue in applications where the fastener is holding important equipment or structures in place. To prevent this, it is important to use a thread-locking adhesive or a locking device like a lock washer or a jam nut.
Another problem associated with coupling nuts is that they may not always align correctly with the threads they are connecting, which can cause difficulty tightening or looseness of the connection. To avoid this, it is important to ensure that the threads are properly aligned before tightening the coupling nut.

What are the advantages of custom connector nuts versus standard options?

Custom-manufactured connector nuts from Trojan Special Fasteners offer several advantages:

Precise thread engagement lengths for optimal performance
Mixed thread types and sizes for specialised applications
Integration of anti-vibration features
Custom materials for specific strength or environmental requirements
Specialty coatings for enhanced performance
Modified geometries to fit tight spaces
Sight holes for visual inspection of thread engagement
Cost-effective solutions for unique applications that would otherwise require complex assemblies

How do you ensure quality in connector nut manufacturing?

At Trojan Special Fasteners, our quality assurance process includes:

Rigorous material traceability
Thread gauge inspection for every batch
Dimensional verification using precision measuring equipment
Surface finish testing and visual inspection
Torque testing when specified
Material certification when required
Full batch testing capabilities
ISO 9001 quality management system implementation

Can connector nuts be used in high-temperature environments?

Yes, connector nuts can be designed for high-temperature applications by:

Selecting appropriate high-temperature materials (certain stainless steels, nickel alloys)
Accounting for thermal expansion in the design
Ensuring compatible thread compounds or lubricants
Adjusting thread clearances as needed for thermal cycling

For extreme temperature environments, please consult with our engineering team to determine the best solution for your application.

Need a Custom Connector Nut?

We routinely produce bespoke connector nuts in batch sizes from one-off prototypes to full production volumes. Get in touch for a fast quote or to discuss your design drawings.

How do I order custom connector nuts from Trojan Special Fasteners?

To order custom connector nuts, you can:

Contact our sales team with your specifications
Send detailed drawings if available
Request a consultation with our engineering team for complex requirements
Provide information about the application environment and loading conditions
Specify quantity requirements and delivery timeframes

We pride ourselves on quick turnaround times for both quotes and finished products.

Why choose Trojan Special Fasteners for connector nuts?

Over 30 years of experience in custom fastener manufacturing
Dedicated technical support throughout the design and manufacturing process
Cost-effective solutions without compromising on quality
Quick turnaround times for both standard and custom orders
Comprehensive material and finish options
UK-based manufacturing for reliable supply and quality control
Small and large batch capabilities
Complete traceability and quality assurance

For more information about our connector nut manufacturing capabilities or to discuss your specific requirements, please contact our team.
They are typically available in two forms, one with a hexagon profile and one with a diameter profile:

Hexagon Connector nut, elongated nut typically 3d, which means that the length is three times the diameter, so an M16 connector nut would be 48mm long.

Round Connector nut, elongated nut typically 3d, which means that the length is three times the diameter, so an M16 connector nut would be 48mm long

Typically they are 3 times the length of the inner diameter, but we can machine other sizes, just ask! We can manufacture these in a limited number of sizes with a square profile if needed – but these are extremely rare. We can make almost any combination of internal and external diameter or profile you’re looking for within available material specifications and finishes. At times customers ask these to be partially threaded on each end, sometimes with mixed thread sizes, pitches and a combination of left hand on one side and right hand on the other. Typically these are known as reducing coupling nuts.

Please be advised that the DIN 6334 standard that is often quoted is incorrect. This was a draft standard in 1943 but was never published as a standard and probably fell into disregard during the war. In various catalogues DIN 6334 is still used today by mistake or as a "sales argument". It must be noted that for this reason no official 'Grade' can be offered or marked for this fastener type and so whilst Trojan Special Fasteners Ltd manufactures these types of coupling nuts in metric thread form, we will always quote the material used.

In addition to standard preferred sizes, we also manufacture non preferred sizes and non standard or special thread and nut forms.

Trojan special fasteners can build additional features into fasteners, like collars, castellated, slotted portions and also cross drill and tap these:

Hex Coupling Nuts with Cross Tapped Sections

Hex Connector or Coupling Nut with 3 points tapped for grub screws. These are elongated nuts typically 3d, which means that the length is three times the diameter, so an M16 connector nut would be 48mm long

ANSI B18.2.2-2015 Table 13 Coupling Nuts. These come with a viewing hole cut across the nut positioned in the middle - this is to see if the mating parts are joined up in the middle or not. Additionally this hole can be used to insert a rod and then help tighten or reposition the nut. These are elongated nuts typically 3d, which means that the length is three times the diameter, so an M16 connector nut would be 48mm long

Connector nut with two tapped holes drilled on the ends for grub screws to tighten against studding. These are elongated nuts typically 3d, which means that the length is three times the diameter, so an M16 connector nut would be 48mm long

Reducing Connector Nuts

Reducing connector nuts or reducing coupling nuts are often used when we need to step down (or step up) from one size to another. They are used to connect two externally threaded parts. For example when one male thread is M16 and we need to couple it with an M12 bolt. This is easily achieved by us - we can mix and match whatever sizes, pitches and fit you prefer. All we ask is that you consider the spanner size that is most appropriate for you and also the overall length, because this determines the amount of thread engagement you will have.

Adapter Nuts

Adapter nuts are typically connector or coupling nuts used when we are changing the thread type from one fastener to another. For example we recently made a nut for a customer who had an 11/16 whitworth threaded bolt to which he was attaching a mount for a machine. The problem was, the newly manufactured mounts only came in a metric thread and it was too expensive and difficult to modify the male threaded part on the mount. Our solution... manufacture a connector nut in EN16T (605M36T material) with an 11/16 BSW thread on one side and M16 coarse thread the other side. We did this in just a few days. Our customer was very happy with the end result.