In applications where shaft systems are subjected to severe alternating impact loads-such as robotic joint axes, servo reducer assemblies, high-speed gearboxes, CNC machine tool feed axes, and rotating pivot points in construction machinery-traditional KM, KMT, and KMD series spindle locking nuts have proven to lack sufficient anti-loosening redundancy under high-frequency impact-vibration composite conditions. Extensive on-site maintenance statistics show that in the KM-type locking structure paired with a retaining washer, the retaining washer is highly prone to plastic creep under conditions of hundreds of alternating impacts per minute. After 300–800 hours of service, deformation of the washer's claws occurs, and the anti-loosening torque decreases by more than 60%. The KMT radial set screw locking nut relies on a single-point compression of the threads by the set screw, which can easily cause localized damage to the thread flanks of the main shaft; after repeated disassembly and reassembly, the thread fit accuracy deteriorates; Conventional round locknuts rely on end-face friction to prevent loosening; however, under impact loads, micro-slip occurs in the threaded pair, causing rapid loss of preload and leading to failures such as increased bearing clearance, abnormal gear meshing noise, rotational play in joints, and loss of positioning accuracy. Traditional locking nut designs struggle to meet the combined demands of high impact loads, repeated assembly and disassembly, high-temperature environments, and operation without additional washers. The Guk Lock Nut, as a precision shaft system locking nut with built-in effective torque, fills this gap in such operating conditions. Based on the GB/T 9160 standard for rolling bearing accessories, the ISO 2982-2 specification for rolling bearing locking components, and the ISO 2320 test standard for effective torque locking fasteners, and drawing on actual failure cases from shaft assembly tests, systematically explains the performance characteristics of the Guk Lock Nut, its composite locking transmission mechanism, structural and material differences, operating condition suitability limits, and precision assembly specifications. This helps engineers select the appropriate thread specifications, precision grades, locking versions, and materials, thereby avoiding engineering issues such as shaft system preload failure, thread damage, and premature fatigue failure of components caused by mismatches.
Guk Lock Nuts are precision locking nuts with built-in effective torque, specifically designed for the axial positioning of bearings, gears, and bushings in shaft systems subjected to high-impact, alternating loads. The main product lines include the Guk-S Standard Series, Guk-H Heavy-Duty Reinforced Series, and Guk-T High-Temperature Series, with sizes ranging from M8 to M160 metric fine-pitch threads and precision grades categorized into Standard and Precision (P-grade) levels. The entire nut is made of alloy structural steel that has undergone forging and tempering, full-body stress-relief aging, thread grinding, and precision grinding of the bearing surfaces. The nut body integrates an elastic locking ring unit, eliminating the need for external anti-loosening components such as stop washers, radial set screws, or friction discs. The precision-ground support end faces ensure uniform axial pressure distribution, while the built-in elastic locking ring generates a radial interference clamping torque with the thread flanks. This dual-mechanism design achieves both axial positioning and circumferential self-locking to prevent loosening, effectively suppressing micro-slip in the threaded pair caused by impact and vibration. It also avoids typical failures associated with traditional locking nuts, such as washer fatigue, damage to the spindle threads caused by set screws, and rapid loss of preload. With end-face runout ≤0.004 mm, thread accuracy of 4H, consistent effective torque, and no need for additional anti-loosening components, it is widely suitable for shaft positioning applications subject to severe shock and vibration, such as industrial robot joints, precision gearboxes, servo reducers, heavy-duty feed shafts, and rotating pivot points in construction machinery.
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Product Highlights
The core characteristics of the Guk Lock Nut include built-in effective torque self-locking, precision-ground bearing surfaces, no external anti-loosening accessories, strong resistance to impact creep, and controllable repeatable assembly/disassembly performance. These are the most fundamental differences between the Guk Lock Nut and the KM/KMT/KMD series spindle locking nuts. Setting aside marketing jargon, extensive bench testing and on-site assembly data have distilled four practical advantages:
Precision-ground bearing contact surfaces ensure uniform axial pressure without off-center loading. For precision-grade products, surface runout is controlled within 0.004 mm. After locking, the inner ring of the bearing and the gear retaining ring are subjected to uniform force around the entire circumference, preventing the generation of additional overturning torque and reducing the risk of radial runout in the shaft system and one-sided bearing overheating.
Grind-grade fine-pitch threaded engagement, with a built-in elastic locking ring that generates stable and effective torque. The thread precision is 4H/5H grade, with minimal thread profile half-angle error; the nut incorporates a heat-treated elastic locking ring. During the screw-in process, the locking ring elastically grips the thread flanks, continuously generating circumferential frictional resistance. This achieves anti-loosening without the need for lock washers or set screws, eliminating the risk of fatigue failure associated with external anti-loosening components.
A wide range of operating conditions is covered by different versions, including standard, heavy-duty, and high-temperature models. The Guk-S standard model is suitable for moderate impact and normal-temperature conditions; the Guk-H heavy-duty reinforced model features an enlarged locking ring cross-section to enhance impact resistance, making it suitable for heavy, alternating loads in construction machinery;Guk‑T is a high-temperature-specific, optimized locking ring material that maintains controllable locking torque decay at 220°C, making it suitable for high-temperature gearbox operating environments.
The base body undergoes full hardening and stress relief, ensuring controllable wear during assembly and disassembly. The base body is normalized, and the locking ring undergoes separate heat treatment; the nut base body has a hardness of HB 240–280, while the locking ring has a hardness of HRC 42–48. Within the specified number of assembly and disassembly cycles, effective torque decay is less than 15%, significantly reducing maintenance and spare part costs compared to one-time-use retaining washers.
At the same time, the operating limits of Guk Lock Nuts are clearly defined: for ultra-high-speed rotating shaft systems, dynamic balance ratings must be verified, and dynamically balanced versions should be prioritized; for stainless steel shafts with a high risk of thread seizing, the threaded assembly area must be coated with a specialized solid lubricant; the locking ring is an elastic, wear-prone component; once the manufacturer's specified number of assembly and disassembly cycles is exceeded, the effective torque will decrease significantly, and it must not be reused; They are not suitable for spindles with damaged or nicked threads, as damaged threads will directly compromise the locking ring's elastic structure; under extreme impact or heavy-load conditions, a single locking nut is insufficient and must be used in conjunction with a disc spring compensation assembly.
Core Operating Principle
The Guk Lock Nut's transmission mechanism differs from that of ordinary nuts, which rely solely on end-face friction to prevent loosening, and from the KM series, which relies on external locking components. It employs a three-in-one composite shaft locking mechanism comprising: axial feed positioning via a precision threaded pair; even load distribution and pressure application across a high-flatness end face; and effective torque self-locking via an internal elastic locking ring. This mechanism addresses three major engineering challenges-loss of preload under severe shock and vibration conditions, fatigue of external anti-loosening components, and localized thread damage-from a mechanical perspective, enabling controlled axial positioning of bearings and gears, maintenance of preload, and resistance to loosening and backslack.
Analyzing the mechanical logic of shaft assembly, the precision external threads of the shaft and the ground internal threads of the Guk nut form a low-clearance precision screw pair. The tightening torque is converted into linear axial thrust through the thread pitch angle. Leveraging the micro-feed characteristics of fine-pitch threads, this system enables micron-level axial displacement adjustment of the bearing inner ring and gear spacer. The precision-ground bearing surface of the nut features high flatness and perpendicularity to the thread axis. Once locked, it applies pressure across the entire bearing surface, preventing stress concentration and misalignment of the bearing inner ring caused by excessive runout of the lower nut's end face. This eliminates, at the source, defects such as unbalanced load wear on rolling elements and amplified rotational runout in the shaft assembly.
During steady-state operation of the equipment, under conditions involving impact, alternating vibration, and thermal expansion, the shaft system generates alternating axial feedback loads, causing the threaded pair to exhibit a tendency toward circumferential micro-slip. The Guk nut relies on a built-in, heat-treated elastic locking ring, whose inner diameter is slightly smaller than the thread's major diameter. Upon screwing in, the locking ring is expanded by the threads, continuously generating a radial elastic clamping force. This creates a stable and effective locking torque at the thread engagement surface, establishing circumferential damping between the nut body and the thread flanks to counteract the loosening torque induced by impact vibrations and suppress microscopic slippage in the threaded pair, thereby maintaining the axial preload over the long term. Compared to the KM stop-ring structure, there is no risk of fatigue fracture in the stop ring; compared to the KMT radial set screw structure, there is no issue of the hard set screw causing compression damage to the main shaft's thread flanks.
When faced with dynamic operating conditions such as fluctuating impact loads during equipment start-up and shutdown, as well as thermal expansion and contraction caused by gearbox temperature rise, this structure-relying on the precision of the threaded fit, the stability of the end-face reference, and the elastic compensation capability of the locking ring-can adaptively offset minor displacement deviations in the shaft system. It maintains the bearing working clearance and gear axial clearance within the design-allowed range, ensuring stable positioning accuracy of the shaft system.
A comparative analysis of the operational shortcomings of various shaft system locking components reveals the following: Ordinary round nuts lack control over positional accuracy, have no self-locking mechanism, and experience rapid loss of preload under impact conditions; they are used only for general fastening applications with no precision requirements. KM-type locking nuts must be used in conjunction with stop washers, which are single-use, wear-prone components prone to fatigue failure under high-frequency impacts; The set screw in the KMT radial set-screw locking nut can damage the main shaft threads, and repeated disassembly and reassembly leads to cumulative thread damage; the KMD double-end-face friction locking nut relies on end-face friction to prevent loosening, but the friction interface is prone to creep and slippage under strong impacts; hydraulic locking nuts offer high preload accuracy but are characterized by high equipment costs and large structural dimensions, making them unsuitable for standardized shaft systems of small and medium sizes. Guk Lock Nuts combine end-face positioning accuracy, built-in self-locking anti-loosening mechanisms, no additional parts, and maintainability, offering irreplaceable comprehensive compatibility advantages in high-impact and vibration environments such as robot joints, gearboxes, and feed axes.
Its core engineering value can be summarized as follows: by utilizing a precision mechanical structure to constrain assembly deviations and dynamic impact deformation, it establishes and maintains a long-term, stable axial preload in the shaft system, eliminates uneven wear on bearings and gears, mitigates the risk of failure in external anti-loosening components, reduces the probability of shaft system failures, and extends the service life of transmission components.
Customer Photos and Feedback
Product Structure and Materials
The Guk Lock Nut features an integral ring-shaped disc structure. It is precision-machined according to four key dimensions: thread accuracy, geometric and positional tolerances of the support end face, elastic properties of the built-in locking ring, and reliability under installation and removal forces. All components undergo multiple rounds of stress-relief aging treatment to eliminate residual stresses resulting from turning, grinding, and locking ring forming processes. Core components include the nut body, precision internal threaded pair, lapped support end faces, built-in elastic locking ring unit, wrench force application structure, and surface treatment layer. Detailed structural parameters are shown in the table below:
| Structural Component | Brief Introduction | Core Requirements |
| Nut Base Body | Main load‑bearing structure for axial load | 40Cr/42CrMo forged; HB240‑280; end‑face flatness ≤0.002mm |
| Precision Internal Thread | Mating reference for coaxiality & feed accuracy | Class 4H; half‑angle ≤30′; Ra≤0.8μm |
| Lapped Supporting Face | Axial pressure reference onto bearing/gear spacer | Runout ≤0.004mm; Ra≤0.4μm; perpendicularity ≤0.006mm |
| Built‑in Elastic Locking Insert | Core self‑locking element generating prevailing‑torque | Spring steel HRC42‑48; ISO2320 5‑cycle verified; no permanent deformation |
| Wrench Engagement Feature | Force‑bearing profile for hook‑spanner assembly | Circumferential hook slots; arc transition; balanced stress, no chipping |
| Surface Treatment Layer | Corrosion protection & stable friction coefficient | Black oxide/phosphating; Dacromet/nickel for salt‑spray; uniform film no thread buildup |
In addition to the standard general-purpose design, specialized variants are available: a dynamic balancing version specifically for high-speed shafts, with overall dynamic balance corrected to G2.5 grade; an ultra-thin, low-profile version suitable for compact shaft systems with limited axial installation space; and a high-temperature Guk-T version featuring a locking ring made of heat-resistant alloy steel, capable of long-term operation in environments ranging from –40°C to 220°C.
Base Material Selection Criteria:
40Cr alloy steel: The primary general-purpose material, offering outstanding cost-effectiveness and suitable for conventional applications such as servo reducers and feed shafts operating at room temperature under moderate impact loads.
42CrMo alloy steel: Designed for heavy-duty impact applications; features higher matrix strength and an enlarged locking ring cross-section, making it suitable for rotating pivot points in construction machinery and heavy-duty robot joints.
Heat-Resistant Spring Steel Combination: Used for long-term high-temperature conditions in gearboxes; accounts for the difference in thermal expansion coefficients between shaft components and nuts to prevent abnormal fluctuations in preload caused by temperature changes.
Key Points for Avoiding Operational Pitfalls: Thread specifications and pitch must match the spindle 100%; do not mix metric fine-pitch threads; Any nicks or burrs on the main shaft thread faces must be repaired, as damaged threads will directly scratch the locking ring; effective torque decreases with each disassembly and reassembly cycle, so strictly adhere to the manufacturer's maximum allowable number of cycles; apply the locking torque strictly according to the specifications in the catalog, as excessive preload will cause permanent failure of the locking ring; high-temperature grease must be used when assembling stainless steel main shafts to prevent thread seizure.
Common Applications and Uses of the Product
Guk Lock Nuts are specifically designed for bearing positioning in shaft systems subjected to severe alternating shock and vibration, axial locking of gear spacers, built-in self-locking to prevent loosening, and reducing the need for external spare parts. They cover four core fields: robotics, gearboxes, CNC machine tools, and construction machinery:
Industrial Robot Joint Shafts: For securing bearings and spacer sleeves on six-axis robot joints and collaborative robot output ends, which are subjected to frequent start-stop impacts. The Guk‑H heavy-duty model reliably controls axial play in the joint to ≤3 μm, eliminating the need for stop washers and reducing equipment maintenance frequency.
Precision servo gearboxes and planetary reducers: Axial positioning of internal bearings and retaining rings in reducers. In the high-temperature environment inside gearboxes, the Guk‑T high-temperature model is adapted to the housing's operating temperature, preventing failures caused by high-temperature creep and loosening of washers.
CNC machine tool feed axes and lead screw support ends: Axial locking of the lead screw bearing housing addresses the alternating impact loads caused by feed direction changes, resolving the vibration-induced loosening issues associated with traditional circular nuts.
Construction machinery pivot points: Bearing positioning in small rotary and swing mechanisms; in outdoor vibration and shock conditions, built-in self-locking structures enhance operational reliability.
In addition, they are widely used in precision rotating components subject to significant shock and vibration, such as heavy-duty rollers in textile machinery, drum shafts in printing equipment, and rotating fixture shaft systems in testing equipment.
Key Points for Precision Assembly
Statistics on shaft system failures indicate that approximately 48% of Guk Lock Nut preload failures stem from non-standard assembly procedures, with damage to the locking ring, thread seizure, and uncontrolled torque being the primary causes. Assembly must strictly adhere to the following four process guidelines: thread cleaning, smooth coaxial insertion, staged torque tightening, and post-assembly performance verification:
Preliminary Cleaning and Parameter Verification
Clean the spindle threads, the internal threads of the nut, and the bearing end faces with clean kerosene to remove metal shavings, burrs, and rust-preventive oil residues; hard particles entering the thread engagement area can scratch the internal locking ring, causing permanent damage to its self-locking capability; Verify the thread specifications, precision grade, and manufacturer-recommended tightening torque. Inspect the nut end face for any dents or indentations and ensure the locking ring shows no visible deformation. Apply the specified solid lubricant evenly to the threads of the stainless steel shaft.
Smooth, Coaxial Pre-assembly Alignment
Manually screw the nut smoothly along the thread, maintaining coaxial alignment throughout the entire process; do not tilt or force it in. It is normal to feel effective resistance from the locking ring during the initial screwing-in phase; do not use a torque wrench to force it in violently, to prevent twisting and damage to the locking ring; Slow down the rotation speed as the nut approaches the end face of the bearing or spacer, and confirm that the support end face is completely parallel to the mating component, with no one-sided or loose contact.
Use a dedicated hook wrench to apply the tightening torque in two equal stages according to the manufacturer's specified torque values; do not tap or force the nut into place. Do not use additional anti-loosening components such as lock washers or set screws during the tightening process. Guk relies on its built-in locking ring for self-locking; adding extra anti-loosening components will alter the original force distribution system.
Closed-Loop Accuracy Verification After Assembly
Use a dial indicator to measure the axial play and radial runout of the shaft assembly to confirm that the values fall within the allowable design range; manually rotate the shaft assembly to ensure that the rotational damping is uniform, with no sticking points or abnormal noises; Conduct 50 no-load start-stop cycles to simulate shock conditions, then remeasure the axial preload. If loosening occurs, disassemble the assembly to inspect the locking ring for damage; do not simply retighten and continue use.
Product Packaging Showcase
Frequently Asked Questions (FAQ)
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Q: The Guk locking nut is very difficult to tighten during assembly. Is this a product quality issue? A: This is normal behavior. Guk relies on a built-in elastic locking ring to generate effective torque, so there will be a constant resistance during the screwing process; however, if the resistance suddenly spikes or the nut becomes completely impossible to turn, it is highly likely that the thread flanks have been damaged or the locking ring has become distorted. In such cases, the nut should be disassembled and inspected; do not attempt to force the assembly.
Q: Why do Guk nuts loosen after operating for a period of time? A: There are four common causes: exceeding the limit on the number of disassembly and reassembly cycles, leading to elastic fatigue of the locking ring; damage or scratches to the locking ring caused by impacts on the spindle thread surface; iron filings or impurities mixed into the threads during assembly, damaging the locking ring's structure; or actual impact loads exceeding the load threshold of the selected model. For heavy-impact, heavy-load applications, we recommend upgrading to the Guk-H heavy-duty reinforced model.
Q: How do you select and distinguish between the Guk-S, Guk-H, and Guk-T series? A: For moderate impact at room temperature and conventional reducer feed shafts, use the Guk-S standard type; for robot joints and construction machinery pivot points subject to frequent, high-impact loads, use the Guk-H heavy-duty reinforced type; for gearboxes operating in long-term high-temperature environments, use the Guk-T high-temperature specialized type.
Q: How many times can a Guk locking nut be repeatedly installed and removed? A: According to ISO 2320 test bench conditions, the Guk-S standard model allows for 8 installations and removals; the Guk-H heavy-duty model allows for 12. Once the maximum limit is reached, the locking ring's elasticity deteriorates, and the effective torque no longer meets design requirements. The nut must be replaced with a new one and cannot continue to be used.
Q: When selecting Guk locking nuts for high-speed applications, which parameters should be given special attention? A: For high-speed shafts with a dn value greater than 800,000, be sure to select the dynamically balanced version; ensure the nut's outer circumference has no protrusions to reduce aerodynamic drag; calculate the nut's moment of inertia; and avoid using ultra-thin, non-standard custom models in high-speed applications, as their insufficient stiffness can easily induce vibration.
Q: Does a higher tightening torque result in better anti-loosening performance? A: No. Exceeding the rated upper limit of the tightening torque will cause permanent plastic deformation of the internal locking ring, directly resulting in the loss of self-locking capability. At the same time, excessive axial preload causes severe bearing overheating and a significant reduction in service life. It is essential to strictly adhere to the torque specified in the product catalog, with a tolerance of ±10%.
Q: Can KM lock washers be used as a direct replacement for Guk locking nuts? A: Direct replacement is not recommended. KM relies on lock washers for anti-loosening; however, these washers are disposable parts that are highly prone to creep failure under high-frequency impact and alternating load conditions. They lack an effective built-in torque self-locking mechanism, resulting in high maintenance and spare part costs. They are only suitable for low- to medium-impact applications and cannot replicate Guk's impact-resistant self-locking performance.
Q: What is the cause of abnormally high temperature rise at one end of the bearing after assembly? A: It is most likely due to misalignment at the nut end face, causing unilateral bearing loading. Another possibility is deformation of the retaining ring caused by excessive preload torque. A complete disassembly is required to inspect the cleanliness of the support end face and check for damage to the retaining ring, followed by reassembly in accordance with specifications. |
References
Technical Specifications for Locking Nuts for Rolling Bearings GB/T 9160.1‑2018
Rolling Bearings-Accessories-Locking Nuts and Stops ISO 2982‑2
Performance Testing of Effective Torque-Type All-Metal Locking Fasteners ISO 2320
Assembly Process Manual for Robot Joint Shaft Locking Components. China Robot Industry Alliance
Failure Analysis and Testing Technology for Precision Shaft System Locking Nuts. Fastener Industry Technical Manual
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