Medium-Strength Steel Nylon-Insert Flange Locknuts

Medium-Strength Steel Nylon-Insert Flange Locknuts

Prevailing-Torque Hex Flange Locknuts for Metric and Inch-Thread OEM Assemblies

JUXIN FASTENERS supplies medium-strength steel nylon-insert flange locknuts for industrial manufacturers requiring vibration-resistant threaded fastening, 

integrated flange support and consistent assembly performance.

These fasteners combine a hexagonal nut body, an integral circular flange and a retained non-metallic locking insert. 

As the mating bolt engages the nylon ring, interference between the insert and the external threads generates prevailing torque that resists unintentional nut rotation.

The flange increases the bearing area beneath the nut and can eliminate the need for a separate flat washer where the joint design permits.

In American industrial markets, common product names include Nylon-Insert Flange Locknuts, Nylon-Insert Flange Nuts,

  Nylon-Insert Flange Lock Nuts and Nylon-Insert Prevailing-Torque Hex Flange Nuts.

The original JUXIN FASTENERS catalog lists metric M5–M20 sizes. Customer-specific UNC and UNF inch-thread configurations can also be reviewed for OEM production.

Product Specifications

What Is a Nylon-Insert Flange Locknut?

A nylon-insert flange locknut is a prevailing-torque fastener that combines a locking insert with a wider bearing surface.

The nylon insert is retained near the top of the nut. When the mating bolt enters the insert, the nylon deforms locally around the bolt threads and creates resistance to rotation.

Unlike an ordinary hex nut, a nylon-insert locknut develops prevailing torque even before the joint is fully clamped.

The integral flange spreads the bearing load over a larger area than a comparable nut without a flange.

Main Engineering Advantages

• Prevailing-torque resistance to loosening.

• Integrated flange bearing surface.

• Reduced need for a separate flat washer in suitable joints.

• Compact fastening arrangement.

• Non-serrated flange options for sensitive mounting surfaces.

• Metric and inch-thread designs.

• Multiple material and coating options.

• Suitable for repeatable industrial assembly processes.

Important Limitation

The locking insert resists nut rotation, but it does not guarantee that the joint will maintain its original clamp force under every vibration or loading condition.

Joint design, preload, bolt strength, temperature and installation procedure remain essential.

How the Nylon Insert Locking Mechanism Works

The locking mechanism relies on interference between the nylon insert and the mating bolt threads.

Installation Sequence

1. The nut initially engages the bolt through its metallic internal thread.

2. The bolt reaches the nylon locking insert.

3. The nylon deforms around the external thread profile.

4. Resistance to rotation develops.

5. The nut continues toward the joint surface.

6. The flange contacts the assembly and clamp force develops as tightening continues.

Prevailing Torque vs. Tightening Torque

Prevailing torque is the resistance generated by the locking feature independently of joint clamp load.

Tightening torque includes the torque needed to overcome thread friction, bearing friction, prevailing torque and the torque contributing to clamp force.

For controlled assemblies, the prevailing-torque contribution must be considered when establishing the installation process.

Engineering Insight

A torque specification developed for an ordinary hex nut should not automatically be transferred to a nylon-insert flange locknut.

Why Use an Integrated Flange?

The integral flange increases the contact area between the nut and the mounting surface.

Potential benefits include:

• More distributed bearing pressure.

• Reduced need for a separate flat washer.

• Improved assembly part-count efficiency.

• Greater coverage around suitable clearance holes.

• Convenient installation in production environments.

Oversized and Irregular Holes

The flange may help bridge a clearance hole larger than the nut body's bearing area.

However, this does not mean the nut is suitable for every oversized, slotted or irregularly shaped hole.

The engineer must evaluate flange diameter, hole dimensions, edge distance, bearing stress and joint movement.

Non-Serrated vs. Serrated Flange Nuts

Engineering Note

A smooth flange may reduce surface marking compared with serrations, but it cannot guarantee a mark-free surface.

Metric Nylon-Insert Flange Locknut Standards

ISO 7043:2012

Prevailing-torque type hexagon nuts with flange, with non-metallic insert, style 2, product grades A and B.

This standard covers metric coarse-thread sizes M5–M20 and property classes 8, 9 and 10.

Product grade A applies through M16, while product grade B applies above M16.

ISO 12125:2012

Prevailing-torque type hexagon nuts with flange, with non-metallic insert, with metric fine-pitch thread.

This standard covers nominal diameters M8–M20 and property classes 6, 8 and 10.

ISO 2320:2015

Specifies functional properties of prevailing-torque steel nuts, including prevailing-on torque, prevailing-off torque and related test requirements.

Important Standards Distinction

ISO 7043 and ISO 12125 apply to different thread series.

The product must be matched to the correct standard, thread pitch, property class and drawing.

Metric Catalog Sizes

These are standard ISO metric coarse-thread designations corresponding to the nominal sizes in the original product information.

Actual availability, tolerance class, material grade and flange geometry must be confirmed for each part.

Metric Fine-Thread Options

Fine-pitch designs may be considered for suitable OEM applications.

Examples of recognized metric fine-thread designations include:

These are engineering thread references, not confirmed standard inventory.

For ISO 12125 applications, the full standard and approved drawing must be checked.

American Inch-Thread Nylon-Insert Flange Locknuts

ASME B18.16.6-2017 (R2022) provides requirements for inch-series prevailing-torque locknuts.

For carbon steel nylon-insert hex flange locknuts, the standard includes an applicable nominal size range of 1/4"–3/4".

UNC – Unified National Coarse

UNF – Unified National Fine

Inch-Thread Availability Notice

The original JUXIN FASTENERS product information lists metric sizes only.

The UNC and UNF dimensions above are American engineering and search references. They do not establish stock availability or manufacturing approval for every configuration.

Custom inch-thread designs can be evaluated from customer drawings and technical requirements.

Metric and Inch Threads Are Not Interchangeable

ISO metric threads and Unified inch threads have different dimensional and pitch specifications.

Examples:

• M6 × 1.0 is not interchangeable with 1/4"-20 UNC.

• M8 × 1.25 is not interchangeable with 5/16"-18 UNC.

• M10 × 1.5 is not interchangeable with 3/8"-16 UNC.

• M12 × 1.75 is not interchangeable with 1/2"-13 UNC.

Thread compatibility must be verified before assembly.

Medium-Strength Steel and Mechanical Property Classes

The original product description identifies medium-strength steel and Grade F.

However, the applicable mechanical classification depends on the thread system and product standard.

Metric Products

ISO 7043 includes property classes 8, 9 and 10.

A specific property class must be verified against the actual product and inspection documentation.

American Inch-Series Products

ASME B18.16.6 uses nylon-insert locknut grades N2, N5 and N8.

These grades should not be confused with the all-metal locking nut grades A, B, C, F and G also addressed by the standard.

Important Grade Clarification

The original description "Grade F" requires confirmation against the intended product specification.

It should not be presented as the verified standard designation for every nylon-insert flange locknut.

Bolt and Nut Strength Compatibility

The mating bolt and nut must be selected for the required joint strength.

Engineering evaluation should include:

• Bolt property class or grade.

• Nut property class.

• Proof load.

• Thread engagement.

• Joint clamp load.

• Prevailing torque.

• Installation torque.

• Service loading.

Material Options

Carbon Steel

The principal material identified for this medium-strength product series.

Stainless Steel

May be evaluated where corrosion resistance is important.

Brass

May be considered for selected applications requiring specific material characteristics.

Aluminum

May be considered for selected lightweight, lower-load applications.

Material Qualification

These materials have different mechanical properties and cannot automatically be supplied to the same carbon steel performance standard.

Material substitutions require engineering approval.

Surface Treatment Options

The original catalog lists:

• Clear/Blue Zinc Plating.

• Color Zinc Plating.

• Zinc-Nickel Plating.

• Dacromet-Type Zinc-Flake Coating.

• Black Zinc Plating.

• Yellow Zinc Plating.

Additional finish options may be evaluated against the customer drawing.

Zinc-Plated Steel

Provides corrosion protection compared with uncoated carbon steel.

Actual performance depends on coating thickness, passivation and exposure.

Zinc-Nickel-Plated Steel

May be selected for more demanding corrosion specifications where an appropriate coating system is available.

Black Oxide

Provides a dark appearance but generally offers limited corrosion protection without additional treatment.

Black Corrosion-Resistant Coatings

Specialized black coatings may provide greater corrosion resistance than conventional black oxide.

However, appearance alone does not establish coating performance.

Important Coating Qualification

No universal 720-hour or 1,000-hour salt spray performance is claimed without an approved specification and verified test report.

Coating and Thread Compatibility

Coating thickness can affect internal thread dimensions, prevailing torque and assembly friction.

For coated locknuts, inspect:

• Thread tolerance.

• Coating thickness.

• Coating continuity.

• Insert condition.

• Prevailing-on torque.

• Prevailing-off torque.

• Functional assembly.

Nylon Insert Temperature Limitations

Conventional nylon inserts have temperature-dependent mechanical properties.

ISO 2320 identifies an application range of approximately −50°C to +120°C for conforming non-metallic-insert prevailing-torque steel nuts.

This is not a universal guarantee for every nylon material or joint.

High-Temperature Considerations

Exposure to elevated temperature may affect:

• Insert stiffness.

• Elastic recovery.

• Prevailing torque.

• Repeated-use performance.

• Long-term locking behavior.

For applications near temperature limits, material selection and functional testing should be reviewed.

Low-Temperature Considerations

Low temperatures may also influence the mechanical behavior of the insert.

Applications with thermal cycling require evaluation of the complete joint.

Are Nylon-Insert Flange Locknuts Reusable?

Some nylon-insert locknuts can be reused under controlled conditions.

However, prevailing torque generally decreases with repeated installation and removal.

Recommended Reuse Assessment

• Applicable standard requirements.

• Remaining prevailing-off torque.

• Insert condition.

• Thread damage.

• Corrosion.

• Temperature exposure.

• Safety requirements.

• Customer assembly procedures.

Engineering Recommendation

For safety-critical or difficult-to-access joints, replacement after removal may be the preferred maintenance requirement.

Do not assume that every nylon-insert locknut is single-use or that repeated reuse is always acceptable.

Prevailing Torque and Vibration Resistance

A nylon-insert locknut creates rotational resistance through interference with the mating bolt.

This can reduce the risk of unintentional loosening in suitable vibration environments.

However, joint reliability depends on:

• Initial clamp load.

• Bolt stiffness.

• Joint stiffness.

• Transverse loading.

• Surface settlement.

• Temperature.

• Insert performance.

• Installation procedure.

Important Limitation

Prevailing torque is not the same as guaranteed clamp-load retention.

Critical applications may require joint-level vibration testing and additional validation.

Installation Engineering Guidelines

1. Verify the Thread

Confirm diameter, pitch and tolerance.

2. Confirm the Mating Bolt

Select a bolt with appropriate strength and thread condition.

3. Inspect the Nylon Insert

Check for damage, contamination or displacement.

4. Confirm Flange Contact

The flange should bear against a suitable joint surface.

5. Use the Approved Tightening Procedure

Account for prevailing torque and friction.

6. Verify Thread Engagement

Ensure sufficient engagement for the required joint performance.

7. Avoid Excessive Heat

Protect the nylon insert from temperatures beyond its validated service conditions.

8. Follow the Reuse Policy

Apply the customer-approved replacement or reuse criteria.

Industrial Applications and Engineering Solutions

1. Automotive Manufacturing

Potential applications include:

• Non-critical vehicle accessory assemblies.

• Production fixtures.

• Inspection equipment.

• Mechanical brackets.

• Industrial assembly equipment.

Engineering Value

Prevailing-torque locking can support reliable fastening where vibration resistance is required and the joint is properly validated.

Safety-critical vehicle connections require additional qualification.

2. Electric Vehicle Manufacturing

Potential applications include:

• EV production equipment.

• Mechanical support brackets.

• Assembly tooling.

• Auxiliary equipment.

Engineering Considerations

Evaluate temperature, vibration, coating compatibility and service requirements.

3. EV Battery Pack Manufacturing

Potential applications include:

• Battery production fixtures.

• Inspection tooling.

• Auxiliary equipment.

• Selected non-electrical mechanical attachments.

Engineering Limitation

These locknuts are not automatically approved for high-voltage electrical connections, battery cell retention or crash-critical structures.

4. Rail Transit Equipment

Potential applications include:

• Interior equipment brackets.

• Maintenance equipment.

• Mechanical housings.

• Non-critical auxiliary assemblies.

Rail applications may require specific vibration, fire, material and safety qualifications.

5. Aerospace Ground Support Equipment

Potential applications include:

• Ground support machinery.

• Inspection fixtures.

• Maintenance equipment.

• Non-flight-critical tooling.

Commercial locknuts are not automatically approved for flight-critical aerospace assemblies.

6. Electrical Cabinets

Potential applications include:

• Mechanical cabinet brackets.

• Mounting assemblies.

• Equipment supports.

• Enclosure accessories.

Engineering Value

The integrated flange can simplify suitable bolted assemblies.

The metallic nut body is electrically conductive and should not be treated as an insulating component.

7. HVAC Equipment

Potential applications include:

• Motor mounting accessories.

• Fan equipment brackets.

• Mechanical support assemblies.

• Equipment housings.

Engineering Considerations

Evaluate vibration, operating temperature, corrosion exposure and maintenance access.

8. Medical Equipment

Potential applications include:

• Non-patient-contact equipment housings.

• Mechanical support brackets.

• Laboratory equipment.

• External accessories.

Engineering Limitation

Cleaning compatibility, material requirements and regulatory qualification must be assessed.

These products are not automatically suitable for MRI or patient-contact applications.

9. Construction Equipment

Potential applications include:

• Equipment housings.

• Machinery brackets.

• Non-critical accessory connections.

• Industrial maintenance assemblies.

Structural applications require appropriate engineering validation.

10. Industrial Machinery

Potential applications include:

• Motor mounting accessories.

• Mechanical equipment brackets.

• Machine housings.

• Vibration-exposed auxiliary assemblies.

Engineering Value

Nylon-insert flange locknuts can combine a locking feature and bearing flange in one component.

11. Robotics and Automation

Potential applications include:

• Robot peripheral equipment.

• Automation fixtures.

• Sensor support brackets.

• Equipment housings.

• Auxiliary mounting assemblies.

Engineering Considerations

Evaluate vibration, dynamic loading, installation torque and maintenance intervals.

12. Sheet Metal Fabrication

Potential applications include:

• Equipment enclosures.

• Metal housings.

• Brackets.

• Mechanical supports.

• Cabinet accessories.

Engineering Considerations

The flange distributes load but does not automatically prevent deformation of thin sheet metal.

Check material thickness, hole geometry and bearing stress.

13. Telecommunications Equipment

Potential applications include mechanical support assemblies, cabinet accessories and non-critical mounting brackets.

14. AI Data Center Infrastructure

Potential applications include mechanical equipment supports, cabinet assemblies and service equipment.

Electrical bonding and grounding requirements must be evaluated separately.

15. Semiconductor Equipment

Potential applications include peripheral machinery, fixtures and selected equipment housings.

Cleanroom contamination and material compatibility requirements must be assessed where applicable.

16. Energy Storage Systems

Potential applications include auxiliary mechanical equipment, manufacturing fixtures and non-critical support assemblies.

High-voltage electrical and safety-critical connections require separate qualification.

17. Power Distribution Equipment

Potential applications include mechanical cabinet assemblies, mounting accessories and equipment supports.

Electrical connection requirements should not be inferred from mechanical locking performance.

18. Industrial Manufacturing Equipment

Potential applications include machinery housings, motor accessories, mechanical brackets and production equipment.

Production Manager Considerations

For production managers, nylon-insert flange locknuts can improve assembly efficiency by combining a locking feature and bearing flange.

Key Evaluation Factors

• Assembly cycle time.

• Reduced washer handling.

• Consistent prevailing torque.

• Automated installation compatibility.

• Tool access.

• Coating friction.

• Thread engagement.

• Insert retention.

• Quality inspection.

• Production lead time.

• Repeat-order consistency.

Quality Control and Inspection

Material Verification

• Carbon steel grade.

• Material certification where required.

• Mechanical property class.

• Lot traceability.

Dimensional Inspection

• Thread diameter.

• Thread pitch.

• Across-flats dimension.

• Nut height.

• Flange diameter.

• Flange thickness.

• Bearing surface geometry.

• Insert position.

Thread Inspection

• Thread tolerance.

• Functional thread fit.

• Mating bolt compatibility.

Prevailing-Torque Testing

• Prevailing-on torque.

• Prevailing-off torque.

• Applicable reuse-cycle performance.

• Test conditions.

• Temperature influence where specified.

Mechanical Testing

• Proof load.

• Thread stripping resistance where required.

• Flange integrity.

• Relevant mechanical properties.

Surface Inspection

• Coating appearance.

• Coating thickness.

• Corrosion test results where specified.

• Surface defects.

• Insert contamination or damage.

Common Engineering Problems and Solutions

Problem 1: Insufficient Locking Torque

Possible causes include insert damage, incorrect insert geometry or repeated reuse.

Solution: Verify prevailing torque against the applicable standard and customer requirements.

Problem 2: Excessive Installation Torque

Possible causes include thread damage, incorrect thread fit or excessive insert interference.

Solution: Inspect the mating threads and locking insert.

Problem 3: Nylon Insert Damage

Possible causes include excessive heat, improper assembly or unsuitable service conditions.

Solution: Review material selection and installation procedure.

Problem 4: Loss of Locking Performance After Reuse

Cause: Reduced insert interference or insert deterioration.

Solution: Apply a validated reuse or replacement policy.

Problem 5: Flange Surface Damage

Possible causes include unsuitable bearing conditions or excessive loading.

Solution: Review flange geometry, joint material and clamp load.

Problem 6: Thread Stripping

Possible causes include incompatible bolt and nut strength or excessive tightening.

Solution: Verify mechanical property compatibility and tightening requirements.

Problem 7: Corrosion

Possible cause: Unsuitable coating or environmental exposure.

Solution: Select a coating system that meets the specified corrosion requirements.

Problem 8: Incorrect Metric or Inch Thread

Cause: Incomplete thread identification.

Solution: Verify the full thread designation before assembly.

Problem 9: Incorrect Mechanical Grade

Cause: Confusion between metric property classes and American nut grades.

Solution: Specify the applicable standard and verified product grade.

Problem 10: Vibration-Related Joint Failure

Possible causes include insufficient clamp load, joint movement or unsuitable fastener selection.

Solution: Validate the complete joint design and vibration performance.

OEM Procurement and Engineering Checklist

For accurate quotation, please provide:

• Product name and part number.

• 2D engineering drawing.

• 3D CAD model, if available.

• Applicable ISO or ASME standard.

• Metric or inch thread.

• Nominal diameter.

• Thread pitch or threads per inch.

• Thread tolerance.

• Mechanical property class or nut grade.

• Carbon steel material specification.

• Nylon insert material requirements.

• Flange diameter.

• Nut height.

• Across-flats dimension.

• Bearing surface requirements.

• Surface treatment.

• Coating thickness.

• Corrosion performance requirements.

• Prevailing-torque requirements.

• Operating temperature range.

• Reuse requirements.

• Inspection and certification requirements.

• Initial purchasing quantity.

• Estimated annual purchasing volume.

• Packaging requirements.

• Delivery schedule.

Custom Nylon-Insert Flange Locknuts for OEM Manufacturing

JUXIN FASTENERS can review customer-specific requirements for:

• ISO 7043 metric coarse-thread designs.

• ISO 12125 metric fine-thread designs.

• ASME B18.16.6 inch-series designs.

• UNC and UNF threads.

• Custom flange dimensions.

• Special nut heights.

• Customer-specified carbon steel grades.

• Selected stainless steel designs.

• Alternative insert materials.

• Zinc plating.

• Zinc-nickel plating.

• Zinc-flake coating.

• Special corrosion-protective finishes.

• Drawing-specific tolerances.

• OEM packaging.

• Production-volume supply.

All configurations are subject to engineering and manufacturing feasibility review.

Frequently Asked Questions

What are nylon-insert flange locknuts called in the United States?

Nylon-Insert Flange Locknuts and Nylon-Insert Flange Nuts are common American product names.

What is the difference between a nylon-insert flange locknut and a regular flange nut?

A nylon-insert flange locknut contains a non-metallic locking element that generates prevailing torque. An ordinary flange nut does not necessarily have a locking feature.

What is the difference between a nylon-insert flange locknut and a serrated flange nut?

A nylon-insert flange locknut uses insert interference to resist rotation. A serrated flange nut uses bearing-surface serrations.

What is ISO 7043?

ISO 7043 specifies metric coarse-thread prevailing-torque hexagon nuts with flange and non-metallic insert.

What is ISO 12125?

ISO 12125 covers corresponding metric fine-thread designs.

What is ISO 2320?

ISO 2320 specifies functional performance requirements for prevailing-torque steel nuts.

What is ASME B18.16.6?

ASME B18.16.6 specifies requirements for inch-series prevailing-torque locknuts, including applicable nylon-insert flange designs.

Is Grade F the correct designation for these nylon-insert flange locknuts?

Not automatically. The applicable grade must be verified against the product design and standard. ASME B18.16.6 identifies N2, N5 and N8 for its carbon steel nylon-insert locknut grades.

What metric sizes does JUXIN FASTENERS list?

M5, M6, M8, M10, M12, M14, M16 and M20.

Can JUXIN FASTENERS supply inch-thread versions?

Customer-specific UNC and UNF designs can be reviewed for manufacturing feasibility.

Are metric and inch threads interchangeable?

No.

Do nylon-insert flange locknuts require a washer?

An integral flange may eliminate a separate flat washer in suitable joint designs. A washer may still be necessary for specific bearing, hole or assembly requirements.

Are nylon-insert flange locknuts reusable?

Reuse may be possible, but prevailing-torque performance can decrease. Follow the applicable standard and customer maintenance requirements.

Can these locknuts be used above 120°C?

Conventional nylon-insert locknuts should not be assumed suitable above the applicable temperature limits. Special materials and engineering validation may be required.

Are these locknuts suitable for vibration?

They provide prevailing-torque resistance to rotation, but the complete joint must be validated for the actual vibration environment.

Are they suitable for automotive and EV equipment?

They may be used in suitable mechanical assemblies and production equipment, subject to the relevant engineering and qualification requirements.

Related Industrial Fastening Solutions

JUXIN FASTENERS also supplies:

• Nylon-Insert Hex Lock Nuts.

• All-Metal Prevailing-Torque Locknuts.

• Serrated Flange Nuts.

• Non-Serrated Hex Flange Nuts.

• Distorted-Thread Flange Locknuts.

• Stainless Steel Locknuts.

• Weld Nuts and Weld Studs.

• Self-Clinching Fasteners.

• Blind Rivet Nuts.

• Threaded Inserts for Plastics.

• Custom CNC Machining Parts.

Internal links should be added only to verified live product pages.

Request an OEM Nylon-Insert Flange Locknut RFQ

JUXIN FASTENERS supports international OEM manufacturers, Tier-1 and Tier-2 suppliers, mechanical engineers, structural engineers, manufacturing engineers,

 production managers, purchasing engineers and global supply chain teams.

For an accurate technical evaluation and quotation, please provide your 2D/3D drawings, thread specifications, required mechanical property class, 

flange dimensions, nylon insert requirements, surface treatment, prevailing-torque criteria, initial purchasing quantity and estimated annual purchasing volume.

Our technical sales team can review dimensional requirements, material selection, metric and inch-thread compatibility, manufacturing feasibility, inspection criteria and production-volume quotations.

JUXIN FASTENERS

Website: https://www.juxinfasteners.com/

Email: info@juxinfasteners.com

Send Your 2D/3D Drawings and OEM Purchasing Requirements for a Nylon-Insert Flange Locknut RFQ.

Packaging Standard

At Juxin Fasteners, we apply standardized export packaging to ensure product protection, traceability, and compliance with international logistics requirements.

1. Standard Export Packaging

Unless otherwise specified, all products will be packed according to our factory standard export packaging, which includes:

Moisture-resistant inner protection

Poly bag or small box packing as required

Reinforced export cartons

Clear labeling with part number, specification, batch number, and quantity

Palletizing for sea or air shipment when necessary

Our standard packaging is designed to ensure safe transportation, efficient warehousing, and long-distance international shipping.

2. Customized Packaging Options

We also provide customized packaging solutions according to customer requirements, including but not limited to:

Private labeling

Customized barcodes

Specific carton dimensions

Retail packaging

Special pallet configuration

Customer-specific marking and identification

So that you know, customized packaging may involve additional costs and extended lead time depending on the complexity of the requirements.

3. Compliance & Quality Assurance

All packaging processes are controlled under our ISO 9001 quality management system to ensure consistency, traceability, and product integrity throughout the supply chain.