SFA Precision Bearing Locknuts with Spanner Slots and Wrench Flats

JX-SFA Precision Bearing Locknuts with Spanner Slots and Wrench Flats

30° Flank-Locking Precision Locknuts for CNC Spindles, Ball Screw Bearing Supports and OEM Shaft Assemblies

Juxin Fasteners is an industrial fastener manufacturer providing standard and custom-engineered fastening components for international 

OEM manufacturers, machine tool builders, precision equipment manufacturers and industrial automation companies.

The JX-SFA Precision Bearing Locknut is designed for accurately positioning and securing bearings, spacers and other mechanical components on threaded shafts.

Its distinctive construction combines a 30° three-point flank-locking mechanism with four peripheral spanner slots and two opposing wrench flats.

This combination provides a precision locking system and multiple installation-tool engagement features.

The JX-SFA series is intended for machine tool spindles, ball screw support units, 

grinding machinery and other shaft assemblies requiring accurate axial positioning and reliable resistance to unintended nut rotation.

Juxin Fasteners supports CNC precision machining, OEM/ODM fastener manufacturing, made-to-drawing metal components and industrial batch production.

JX-SFA Product Technical Specifications

The actual dimensions, thread pitches, manufacturing grade and locking screw specifications must be confirmed against the approved product drawing.

What Is a JX-SFA Precision Bearing Locknut?

The JX-SFA is a precision shaft-retaining nut that combines thread-flank locking with dedicated external installation features.

The nut is positioned on a threaded shaft to retain a bearing inner ring, spacer or other designated component.

Once the required axial position has been established, the locking screws are tightened to engage the phosphor bronze locking components with the mating shaft thread flanks.

This action generates frictional resistance against unintended nut rotation.

Unlike conventional hex locknuts, the JX-SFA is specifically intended for precision mechanical assemblies where thread accuracy, locating-face geometry and installation control are important.

JX-SFA External Geometry: Four Spanner Slots and Two Wrench Flats

A distinctive feature of the JX-SFA design is its external installation geometry.

The series incorporates four peripheral spanner slots and two opposing wrench flats.

Four Peripheral Spanner Slots

The peripheral slots provide engagement features for a compatible hook spanner or other specified installation tool.

Their positions and dimensions must match the approved drawing.

Two Opposing Wrench Flats

The opposing flats provide an additional wrench-engagement option.

This may be useful when assembly space, tool availability or maintenance access favors a flat-jaw wrench.

Why the Combined Geometry Matters

Machine builders often face installation constraints involving adjacent bearings, housings, spacers and shaft shoulders.

The combination of spanner slots and wrench flats provides alternative installation-tool engagement features.

However, tool compatibility depends on the actual nut geometry and available clearance.

The two features must not be assumed to support identical installation torque without engineering verification.

How 30° Three-Point Flank Locking Works

The JX-SFA locking mechanism uses three locking positions distributed around the nut circumference.

The locking components engage the mating shaft thread flanks at an approximately 30° inclination relative to the specified radial reference.

When the locking screws are tightened, the phosphor bronze components are driven toward the mating thread flanks.

The resulting contact creates resistance to loosening.

The three-point arrangement distributes locking action around the circumference.

The actual locking force depends on the screw torque, insert geometry, thread fit and shaft material.

Why Thread-Flank Locking Is Different from Direct Set-Screw Locking

A conventional direct set-screw arrangement may concentrate force at the tip of a screw contacting the shaft.

In a precision flank-locking arrangement, a shaped locking component provides the interface between the locking screw and the shaft thread.

This design can help reduce concentrated contact damage when properly engineered and installed.

The JX-SFA should therefore be distinguished from simple radial set-screw nuts and general-purpose prevailing-torque nuts.

Phosphor Bronze Locking Components

The specified locking component material is phosphor bronze.

These components provide the contact interface between the locking screws and the mating shaft thread flanks.

Relevant engineering considerations include:

• Locking component geometry.

• Thread-flank conformity.

• Contact pressure distribution.

• Resistance to local thread damage.

• Locking screw torque.

• Repeated installation and removal.

The actual phosphor bronze alloy and insert dimensions must follow the approved specification.

Property Class 12.9 Locking Screws

The JX-SFA specification identifies Property Class 12.9 locking screws.

These screws actuate the locking components.

Their property class does not establish the load capacity of the complete locknut assembly.

The appropriate tightening torque must be determined for the actual size and locking configuration.

42CrMo Forged Alloy Steel

The specified JX-SFA body material is 42CrMo forged alloy steel.

This chromium-molybdenum alloy steel is used in precision mechanical components where controlled strength, toughness and machinability are required.

Related material references include DIN 42CrMo4, JIS SCM440 and AISI 4140.

These designations must not be considered automatically interchangeable without checking the applicable chemical composition, heat-treatment condition and mechanical requirements.

Quenched-and-Tempered Hardness: HRC 28–32

The specified hardness range is HRC 28–32.

The heat-treatment condition affects mechanical properties and dimensional stability.

For precision bearing locknuts, heat treatment and machining must be coordinated to achieve the required thread accuracy and locating-face geometry.

ISO 4H Precision Internal Threads

The JX-SFA specification identifies ISO metric internal thread tolerance class 4H.

This tolerance requirement is relevant to the dimensional fit between the nut and the mating shaft thread.

The complete thread designation must include:

• Nominal diameter.

• Thread pitch.

• Internal thread tolerance.

• Mating shaft thread tolerance.

ISO 4H does not independently guarantee locating-face runout or bearing preload accuracy.

Precision-Ground and Precision-Turned Locating Faces

The JX-SFA technical specification identifies locating-face runout requirements from 0.002 mm to 0.005 mm, depending on manufacturing grade.

These values correspond to approximately 2 and 5 micrometers.

The applicable tolerance must be specified for the selected product size.

The engineering drawing must define the measurement datum and inspection method.

Why Locating-Face Runout Matters

A precision bearing locknut may contact a bearing inner ring or precision spacer.

If the locating face is not sufficiently perpendicular to the shaft reference, uneven contact can occur.

Potential consequences include:

• Bearing positioning variation.

• Uneven contact pressure.

• Preload inconsistency.

• Additional assembly adjustment.

• Reduced rotating-system accuracy.

The required tolerance depends on the bearing arrangement and application.

Metric Precision Locknut Size Range

The existing JX-SFA product specification identifies a nominal metric size range from M10 to M420.

Individual thread pitches and external dimensions must be confirmed from the corresponding product drawings.

Metric Fine-Thread Engineering References

These are industry engineering references, not a complete verified JX-SFA stock-size list.

The actual thread designation and product geometry must follow the approved JX-SFA drawing.

Large-Diameter Metric Engineering References

These values are nominal diameter conversions only.

They do not define the thread pitch, outside diameter, axial thickness or available locking configuration.

The large-diameter range must be verified against the applicable product drawings before quotation.

American Inch-Series Precision Locknut References

American OEM manufacturers may specify Unified inch-series threads for precision shaft assemblies.

Juxin Fasteners can evaluate custom inch-series precision bearing locknuts based on customer drawings.

These Unified thread references are for custom engineering evaluation.

They are not confirmed standard JX-SFA stock configurations.

Metric and Inch Threads Are Not Interchangeable

Metric, UNC, UNF, UN, BSW and BSF thread systems must be evaluated independently.

For example:

• M10 × 0.75 is not interchangeable with 3/8-24 UNF.

• M12 × 1.0 is not interchangeable with 1/2-20 UNF.

• M20 × 1.0 is not interchangeable with 3/4-16 UNF.

• M25 × 1.5 is not interchangeable with 1-12 UNF.

Similar nominal diameters do not establish thread compatibility.

Application 1: CNC Machine Tool Spindle Bearings

CNC machine tool spindles require accurate positioning and retention of bearing inner rings and associated shaft components.

JX-SFA precision locknuts may be evaluated for:

• CNC machining center spindles.

• Milling machine spindle assemblies.

• Precision turning spindles.

• Grinding machine spindle bearings.

• Machine tool shaft-retention systems.

Important selection criteria include locating-face runout, bearing preload, locking performance and installation-tool clearance.

Application 2: Ball Screw Fixed-End Bearing Supports

Ball screw fixed-end bearing supports often require precise axial positioning of the support bearings.

The JX-SFA may be used to retain the bearing arrangement on a compatible threaded shaft end.

Relevant applications include:

• CNC feed-axis systems.

• Ball screw support bearing assemblies.

• Precision linear motion equipment.

• Automated positioning systems.

• Industrial actuators.

The nut must match the shaft-end thread, bearing arrangement and required preload.

Application 3: Precision Grinding Machinery

Precision grinding equipment may require tight control of spindle geometry and bearing positioning.

The JX-SFA can be evaluated where the combined spanner-slot and wrench-flat installation features are compatible with the assembly.

Locating-face runout and locking performance must meet the machine designer's requirements.

Application 4: Industrial Automation and Robotics

Potential applications include:

• Precision motion-control assemblies.

• Servo-driven mechanical systems.

• Automated positioning equipment.

• Industrial robot transmission components.

• Rotary indexing mechanisms.

The complete shaft assembly must be evaluated for vibration, axial loading, operating speed and maintenance requirements.

Application 5: Precision Gearboxes and Industrial Transmissions

Precision gearboxes may require accurate bearing retention and shaft-component positioning.

JX-SFA locknuts may be considered for compatible threaded shaft arrangements.

Engineering review should include:

• Shaft thread geometry.

• Bearing arrangement.

• Axial loading.

• Thermal expansion.

• Assembly accessibility.

• Locking reliability.

Application 6: Heavy Industrial Equipment

Larger precision locknuts may be relevant to selected industrial shaft-retention applications.

However, a larger nominal thread diameter does not automatically establish a specific load rating.

The actual allowable axial load must be confirmed for each product size and complete assembly.

JX-SFA vs. JX-SF vs. F-Type Precision Locknuts

All three product families may use 30° flank-locking principles.

Their product pages should therefore be differentiated using verified geometric and installation features rather than unsupported performance claims.

The exact dimensional and structural differences must be verified using the corresponding drawings.

These products must not be assumed interchangeable.

Engineering Selection Guide

Installation and Assembly Procedure

The JX-SFA must be installed according to the approved engineering drawing and bearing manufacturer's instructions.

A typical installation process includes:

1. Verify the shaft thread diameter and pitch.

2. Inspect the nut and shaft threads.

3. Clean the bearing locating surfaces.

4. Select a compatible spanner or wrench for the nut geometry.

5. Install the nut onto the threaded shaft.

6. Establish the required bearing position or preload.

7. Tighten the three locking screws according to the approved sequence and torque.

8. Verify the final axial position and locking condition.

Do not apply an arbitrary locking screw torque.

The correct tightening procedure depends on the actual product size and locking configuration.

Bearing Preload and Axial Rigidity

Precision bearing locknuts are often used in assemblies where bearing preload affects stiffness and operating accuracy.

The required preload depends on:

• Bearing type.

• Bearing arrangement.

• Shaft and housing fits.

• Spacer dimensions.

• Thermal expansion.

• Operating speed.

• Axial loading.

• Assembly procedure.

The JX-SFA must be evaluated as part of the complete bearing system.

The locknut alone does not guarantee zero backlash in a ball screw transmission.

Vibration Resistance and Locking Reliability

The three-point flank-locking mechanism provides mechanical resistance to unintended nut rotation.

Actual locking performance depends on:

• Locking screw torque.

• Phosphor bronze insert geometry.

• Shaft thread material.

• Thread accuracy.

• Nut body material.

• Operating vibration.

• Maintenance condition.

Any required vibration or loosening performance must be validated for the intended application.

Maintenance and Reuse

A properly designed flank-locking precision nut may be suitable for repeated assembly and disassembly.

Before reuse, inspect:

• Internal threads.

• Shaft threads.

• Locking screws.

• Phosphor bronze locking components.

• Locating face.

• Spanner slots.

• Wrench flats.

• Surface condition.

Reuse is permitted only when the components meet the approved inspection criteria.

Unlimited reuse must not be assumed.

Common Engineering Problems and Solutions

Juxin Fasteners Manufacturing Capabilities

Juxin Fasteners is an industrial fastener manufacturer with manufacturing capabilities that include:

• Cold heading.

• Cold forming.

• CNC machining.

• Product-specific secondary operations.

• OEM/ODM custom fastener manufacturing.

• Made-to-drawing precision metal components.

• Industrial batch production.

For JX-SFA precision bearing locknuts, CNC machining and control of the internal threads, locating faces, spanner slots, wrench flats and locking component geometry are particularly important.

The actual manufacturing route depends on product size, geometry, material, tolerances, heat treatment and production volume.

Not every JX-SFA component necessarily uses every process available within Juxin Fasteners' broader manufacturing capabilities.

OEM/ODM Custom Precision Bearing Locknut Manufacturing

Juxin Fasteners supports customer-specific precision locknut projects based on approved 2D drawings and 3D CAD models.

Potential customization includes:

• Metric fine-thread dimensions.

• Custom Unified inch-series threads.

• Special nut outside diameters.

• Custom axial thickness.

• Alternative spanner slot dimensions.

• Customer-specific wrench-flat geometry.

• Special locking screw arrangements.

• Custom phosphor bronze locking components.

• Precision-turned locating faces.

• Precision-ground locating faces, subject to feasibility.

• Material and heat-treatment requirements.

• Surface finishing requirements.

• Special inspection criteria.

• OEM part identification.

• Industrial batch packaging.

All custom specifications are subject to engineering and manufacturing feasibility review.

Quality Inspection and Acceptance

A project-specific inspection plan may include:

• Material verification.

• Hardness testing.

• Internal thread gauge inspection.

• Thread pitch measurement.

• Nut body dimensional inspection.

• Spanner slot inspection.

• Wrench-flat dimensional inspection.

• Locating-face runout measurement.

• Locking screw inspection.

• Phosphor bronze insert inspection.

• Surface finish verification.

• Functional locking evaluation.

The actual inspection scope and acceptance criteria must be agreed against the approved drawing and purchasing requirements.

Engineering Standards and References

ISO 261 and ISO 724

Relevant to ISO metric thread designations and basic dimensions.

ISO 965 Series

Relevant to ISO metric screw-thread tolerance requirements, including the specified internal thread tolerance class 4H.

ASME B1.1

Relevant to Unified inch-series threads used in customer-specific shaft designs.

Material Requirements

42CrMo alloy steel, heat treatment and HRC 28–32 hardness must be defined according to the approved material specification.

Customer Engineering Drawings

The approved JX-SFA drawing must define the locking geometry, spanner slots, wrench flats, internal threads, locking components and locating-face runout.

Similarity to another manufacturer's precision locknut does not establish dimensional interchangeability or identical load capacity.

Frequently Asked Questions

What is a JX-SFA precision locknut?

It is a precision bearing locknut featuring 30° three-point flank locking, peripheral spanner slots and opposing wrench flats.

What is the American engineering name for this product?

Precision Bearing Locknut with Locking Pins and Flank-Locking Precision Locknut are relevant industry terms.

How does the locking mechanism work?

Three locking screws actuate phosphor bronze components that engage the mating shaft thread flanks.

What makes the JX-SFA different from a standard round locknut?

Its combination of four spanner slots, two opposing wrench flats and a precision flank-locking mechanism.

What material is specified?

42CrMo forged alloy steel.

What hardness is specified?

HRC 28–32.

What internal thread tolerance is specified?

ISO metric 4H.

What locating-face runout is specified?

0.002–0.005 mm, depending on the manufacturing grade and approved drawing.

What is the stated metric size range?

M10–M420, with actual thread pitches and dimensions subject to product drawing verification.

Can the JX-SFA be used for CNC spindle bearings?

It may be suitable where the shaft thread, bearing arrangement, runout requirement and locking performance have been verified.

Can it be used for ball screw bearing supports?

Yes, when the dimensions and bearing assembly requirements are compatible.

Can Juxin Fasteners manufacture custom inch-series designs?

Customer-specific Unified inch-series precision locknuts can be evaluated for manufacturing feasibility.

Does the JX-SFA contain ball screw raceways?

No. The JX-SFA is a shaft-retaining locknut, not the recirculating ball nut of a ball screw assembly.

Can JX-SFA locknuts be reused?

Reuse depends on the condition of the threads, locking components, screws and locating surfaces.

Request a Quote — JX-SFA Precision Bearing Locknut Manufacturer

Juxin Fasteners manufactures industrial fasteners and precision metal components for global OEM manufacturers, 

Tier-1 and Tier-2 suppliers, machine tool builders and industrial automation companies.

We support made-to-drawing JX-SFA precision locknut projects for spindle bearing assemblies, ball screw support units, precision transmissions and custom shaft-retention systems.

Recommended RFQ Information

• 2D engineering drawing or 3D CAD model.

• JX-SFA model and required geometry.

• Shaft thread diameter and pitch.

• Metric or Unified inch thread system.

• Internal thread tolerance.

• Nut outside diameter and axial thickness.

• Spanner slot dimensions.

• Wrench-flat dimensions.

• Locking screw dimensions and property class.

• Phosphor bronze locking component requirements.

• 42CrMo material specification.

• Heat treatment and hardness requirements.

• Required locating-face runout.

• Surface treatment requirements.

• Bearing arrangement and axial loading.

• Installation and locking torque requirements.

• Inspection and functional acceptance criteria.

• Initial order quantity and annual purchasing forecast.

• Packaging and delivery requirements.

Please send your engineering drawings and purchasing specifications for technical review and manufacturing quotation.

Juxin Fasteners

Industrial Fastener Manufacturer | OEM/ODM Fastener Manufacturing | CNC Precision Components | Made-to-Drawing Industrial Fasteners

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

Email: info@juxinfasteners.com

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.