Precision Locknut Questions, Answered

NIKKI manufactures its own locknuts rather than sourcing them, holds 0.002 mm maximum axial run-out on grinding grade and 0.005 mm on precision-turning grade, and puts the machining grade into the model code so the precision you are buying is legible before you send an enquiry. Threads are ISO 4H across every series, in SCM440 / 42CrMo4 at HRC 28-32 on the standard range, with MRS in fully stainless SUS304.

Most competitor codes mark only the nut type, which leaves the grade to be confirmed by email before anyone can quote.

Grade for grade the specification is the same: a NIKKI ground nut at 0.002 mm run-out does the same job to the same thread class as a European or Japanese ground nut, and the price difference tends to reflect overhead and distribution rather than process capability. Where NIKKI differs from most of the field is contact face finishing. A refined grinding process leaves a smoother and more uniform contact surface than standard grinding, which shows up as better face contact, tightening stability, and dynamic rotational stability on spindles and high-speed assemblies.

NIKKI is a manufacturing brand. HSIANG KAI FU CO., LTD. has produced precision locknuts in Taichung since 1994, and product design, development, and outer thread grinding are all handled in-house. That means process questions get answered directly: which operations run in-house, what happens to a part that measures out of tolerance, whether a drawing can be quoted instead of a catalog number.

Metric threads from M5 x 0.5 to M260 x 4, with outside diameters from 12.5 to 320 mm, across the 30° flank locking, ultra-uniform locking, radial locking and axial locking series. Left-hand threads are ordered by adding L to the code. Inch threads replace the metric pitch with the TPI, for example HKF30-U18. The range is wide enough to carry a whole machine, so the spindle nut and the gearbox nut can come from one source with consistent finish and locking behavior.

Yes. Alongside the catalog series NIKKI takes ODM projects, custom locknut designs, and outer thread grinding work, and supplies collar and socket mounting tools for accurate assembly of the nuts themselves. Send the shaft thread specification, the axial and radial envelope, the run-out needed at the contact face, and the locking direction, with a drawing if you have one. Quantity and tooling terms depend on the part, so it's worth raising them early rather than at the quotation stage.

The series locks at NIKKI's special flank angle instead of the conventional 30° contact. This keeps the difference between locking torque and thread surface pressure within 10%, a level of uniformity a fixed 30° flank doesn't reach, which prevents loosening, overheating, and noise more reliably.

When torque and flank pressure diverge, parts of the thread carry more load than others. Under vibration and speed, that unevenness allows micro-movement at the contact, and the nut gradually backs off. Holding pressure uniform across the flank removes the mechanism that starts the loosening.

No. Both series lock through set screws acting on the flank angle, so no thrust washer or keyway is required. This simplifies assembly and avoids cutting a keyway into the shaft.

Yes, both series are reusable if handled properly. They're designed for easy assembly and disassembly, which suits maintenance work on spindles and bearing arrangements.

Both series are machined from JIS SCM440 chromium-molybdenum steel (DIN 42CrMo4) at HRC 28-32, with thread and contact surface ground to ISO 4H thread precision.

Often, since HKF covers standard metric fine threads from M15 x 1 to M200 x 3, and its flank locking needs no keyway or tab washer. Confirm the outside diameter and height against the dimension table, as the envelope differs from KM dimensions.

Add L to the order code for a left-hand thread (HKF30x1.5P-L) or U for an inch thread (HKF30-U18). Standard right-hand metric versions are ordered by the plain name.

HKR suits assemblies where axial space is limited. It's the low-profile version of the same series, with body heights from 8 mm against HKF's 14 mm, using smaller set screws at the small end of the range.

Body height runs from 8 mm at M15 x 1 to 32 mm at M200 x 3. That's 6 mm thinner than the equivalent HKF at the small end of the range, which is often the difference between fitting a shallow bearing housing and redesigning it.

HKF suits assemblies where axial space isn't the constraint. It's the standard-height version of the same series, with larger set screws at the small end of the range, M5 against HKR's M4 at M15, for higher locking torque.

Each set screw drives a brass pad that presses against the thread flank of the shaft at a 30° radial angle. The pad grips the flank rather than the thread crest, which gives enough holding force to resist vibration without deforming the shaft. No slot, washer, or tab is needed.

They lock identically, with the same 30° flank, the same materials, and the same 0.002 mm run-out. What differs is the outer profile and therefore the wrench access. MF has a sloped outer face, so when the housing covers part of the nut a hook wrench has trouble seating. BF's straight profile stays usable in that situation. Choose by how much of the nut your housing leaves exposed.

Grinding grade (MF, BF, TMF) has both the thread and the contact face ground, holding maximum axial run-out to 0.002 mm. Precision-turning grade (SFZ, MFZ, BFZ) is finished by precision turning at 0.005 mm, and costs less. Material, hardness, and ISO 4H thread class are the same on both. The grade is in the model code: a Z means precision turned, so MFZ is the turned version of MF.

Choose the Ultra-Uniform Locking Series when preload stability sets the limit on the machine, typically machine tool spindles, ball screws, and high-speed rotating assemblies. Those locknuts lock at an optimized flank angle rather than 30°, keeping locking torque and surface pressure within 10% of each other. For general machinery, the 30° flank series does the job at lower cost.

A pin wrench engages the holes in the face of the TMF and turns the nut down against the bearing. The set screws are then tightened in turn to lock it. Nothing has to reach the outside diameter, so the nut works in housings that give a hook wrench no purchase.

No. TMF is ground only, at 0.002 mm maximum axial run-out. Where a drawing allows 0.005 mm and the cost of the turned grade matters more than the run-out, MFZ and BFZ are the precision-turned types in this series, though both are hook-wrench profiles rather than pin-driven.

MFZ and MF share the same dimensions, the same outer profile and the same SCM440 material at HRC 28-32. The difference is the finishing process. MF is ground to 0.002 mm maximum axial run-out, MFZ is precision turned to 0.005 mm and costs less. A Z in the model code means the turned grade.

Choose BFZ where the housing covers part of the nut. BFZ is the same turned grade at 0.005 mm, in a straight outer profile that still gives a hook wrench something square to seat against. MFZ suits the nuts that sit clear of the housing, and it goes one size smaller, to M12 x 1.

BFZ and BF share the same dimensions, the same straight outer profile and the same SCM440 material at HRC 28-32. The difference is the finishing process. BF is ground to 0.002 mm maximum axial run-out, BFZ is precision turned to 0.005 mm and costs less. A Z in the model code means the turned grade.

SFZ carries two parallel flats for an ordinary open-end wrench, listed as dimension L in the table. The flats run up to SFZ75 x 2.0P, which is the largest size that has them. Above that size the table gives no L dimension.

Choose the ground types where the drawing calls for 0.002 mm rather than 0.005 mm axial run-out, or where the thread runs above M200 x 3. The MF locknut and BF cover metric threads to M260 x 4 in the ground grade, both driven by hook wrench rather than open-end wrench.

Each set screw in a NIKKI radial locknut meets the shaft at 90° and drives a brass pad against the thread flank. The pad grips the flank rather than the thread crest, which gives enough holding force to resist vibration without deforming the shaft. No slot, washer, or tab is needed, and the nut can be taken off and refitted.

MR carries three set screws at 120°, with three hook slots below M105 and six above. SR carries two set screws and four slots at every size, and takes heavier screws at the large end, M12 at 60 Nm from SR135 where MR stays at M10 and 36 Nm.

Both are ground to 0.002 mm in SCM440 at HRC 28-32. MR continues to M260 x 4, while SR stops at M200 x 3.

Choose the 30° Flank Locking Series where the housing has room for a taller nut and nothing is gained by a shorter one. Those types run 14 to 40 mm high, where a radial nut on the same thread is typically a third to a half shorter.

Where preload stability rather than height sets the limit on the machine, look at the Ultra-Uniform Locking Series.

Both lock the same way in SCM440 at HRC 28-32. MR is ground to 0.002 mm maximum axial run-out, MRZ is precision turned to 0.005 mm and costs less. Dimensionally the two match from M40 x 1.5 upward, with M165 x 3 the one exception, but below M40 the MR body runs a few millimeters larger in outside diameter, so the grades are not always interchangeable in a tight bore at the small end of the range.

Choose the SR locknut where the clamping load is better carried by two heavier screws than three lighter ones, since SR takes M12 at 60 Nm from SR135 where MR stays at M10 and 36 Nm. Choose the MRRA locknut for high radial torque, where a taller body and a larger outside diameter on the same shaft thread are worth the extra envelope. MR remains the type to specify above M200 x 3, as neither SR nor MRRA goes that far.

Choose the SRZ locknut where two heavier screws suit the duty better than three lighter ones, or where four hook slots give the wrench a better seat than three. Choose the MRS locknut where the nut has to be stainless throughout, for food, pharmaceutical, chemical or semiconductor equipment. MRS matches the MRZ dimensions across its range, which runs to M50 x 1.5.

MRS is JIS SUS304 stainless steel throughout, and that includes the locking pin and the set screws. The other radial types drive a brass pad onto the thread flank; MRS drives a stainless pin instead, so the nut introduces no second metal into a stainless assembly. Thread precision is ISO 4H, as on the rest of the series.

Dimensionally, yes. MRS matches MRZ across its whole range, from M6 x 0.5 to M50 x 1.5, so the housing needs no change. The materials are not equivalent, though. MRZ is SCM440 hardened to HRC 28-32 and MRS is unhardened SUS304, so MRS is the choice where the environment calls for stainless rather than where the load is high. Get in touch if the application sits near the limit.

MRS runs from M6 x 0.5 to M50 x 1.5, in outside diameters from 16 to 70 mm and body heights from 8 to 14 mm. Above M50 x 1.5 the radial series has no stainless type, so a larger stainless thread is a custom enquiry rather than a catalog item.

SRZ and SR are dimensionally identical across the whole range, in the same SCM440 material at HRC 28-32, with the same two set screws and four hook slots. The difference is the finishing process. The SR locknut is ground to 0.002 mm maximum axial run-out; SRZ is precision turned to 0.005 mm and costs less. A Z in the model code means the turned grade.

Both are turned to 0.005 mm and both lock radially. The MRZ locknut spreads the clamping load over three screws at 120° rather than two, lists pitch options SRZ does not, and carries a d1 diameter in its table. SRZ is the one to specify where two heavier screws suit the duty better, or where a fourth hook slot gives the wrench a workable seat.

The two numbers are the thread and the outside diameter, not the thread and the pitch used elsewhere in the range. MRRA50/75 is an M50 x 1.5 thread in a 75 mm body, and MRRA50/92 is the same thread in a 92 mm body. Add L for a left-hand thread (MRRA50/75-L) or U for an inch thread (MRRA50/75-U18).

The larger diameter puts more material and a wider contact face around the same shaft thread, which is what lets the nut take higher radial torque. It costs axial length and bore clearance to get it. At M30 x 1.5 the choice runs between a 52 mm body 22 mm high and a 65 mm body 30 mm high, so the housing bore usually settles which one you can fit.

No, and it isn't meant to be. The other six types trade holding force for a short body; MRRA does the reverse. At M50 x 1.5 it stands 25 mm high in the 75 mm body and 32 mm in the 92 mm body, where MR is 14 mm and even the 30° flank MF is 20 mm. Specify the MR locknut or the SR locknut where axial length is the constraint, and MRRA where the torque is.

MRN carries two parallel flats for an ordinary open-end wrench, given as dimension L in the table, from 11 mm on MRN05 up to 50 mm on MRN40. Every size in the range has them, so no hook wrench is needed at any point; MRN is the only type in the radial series drawn that way.

MRN05 covers M5 x 0.5 in a body 12.5 mm across and 5 mm high, which is the smallest locknut NIKKI makes. The next size, MRN06, takes M6 x 0.75 at 13.5 mm. Below M6 x 0.5 no other type in the radial series offers anything at all.

Only at the small end. Through M8 x 1 and below MRN is the shorter nut, and from M10 x 1 to M15 x 1 the two stand level at 8 mm. Above that the wrench flats need body, and MRN grows: 25 mm high at M40 x 1.5 against 14 mm for the MR locknut. Specify MRN for the access and the small sizes, not for minimum height.

The locking screws enter through the front face of the nut and run parallel to the shaft, so the hex key approaches head-on and never needs to reach the flank. That allows the nut to be locked and released in a recessed bore or a closed housing. No thrust washer or keyway is required, and the nut can be taken off and refitted.

MA is ground on the thread area as well as the contact surface and holds 0.002 mm axial run-out, locking with two set screws that take up to 56 Nm. MKR grinds the contact surface, holds 0.005 mm, and locks with three to eight clamping screws taking up to 25.5 Nm. MKR carries 58 sizes against MA's 33, including every thread below M17.

The MKR dimension table gives a helical angle for every size, from 2.48° at M12 x 1.5 down to 0.28° at M200 x 3. It corresponds to the lead angle of the thread, so the axial travel of the nut can be worked out from how far it has been turned. On a preloaded bearing arrangement that relationship is what you are setting, and having it on the datasheet saves calculating it from the pitch and the effective diameter each time.

Choose the Radial Locking Series where the outside diameter is still reachable after assembly and axial length is what the design has run out of. Those nuts stand around half the height of a 30° flank body and lock through set screws meeting the shaft at 90°. For general machinery with room around the nut, the 30° Flank Locking Series is the cheaper route, and where preload stability sets the limit on the machine, look at the Ultra-Uniform Locking Series.

Choose the MA locknut where the drawing calls for 0.002 mm axial run-out, since MA has the thread area ground alongside the contact surface, or where two heavy set screws suit the design better than several light ones, as MA reaches M12 at 56 Nm. Choose the MKK locknut where the clamping force matters more than the size coverage, as MKK carries screws to M10 at 36 Nm. MKR remains the type to specify below M15, which neither of the others reaches, and wherever the thread falls between the usual steps.

It is the body height in millimeters. MKW40-28 stands 28 mm high and MKW40-44 stands 44 mm, on the same M40 x 1.5 thread. Most threads up to M50 are listed in two heights, and M55 to M70 are offered at 46 mm only.

Yes, on every thread offered in both heights. At M30 x 1.5 the 28 mm body has a 52 mm outside diameter and the 44 mm body has 68 mm; at M45 x 1.5 the figures are 70 and 90 mm. Check the outside diameter against the housing bore, not the height alone.

Choose the MKK locknut where the assembly needs a short body or more clamping force, since MKK stands 18 to 32 mm high and takes screws to M10 at 36 Nm against MKW's M5 at 9 Nm. Choose the MKR locknut where the thread sits outside MKW's range, which covers only M20 to M70 on a 1.5 mm pitch, or where an intermediate thread is needed. MKW is the type to specify when the design wants the length, whether for thread engagement or to fill space a separate ring would otherwise occupy.

It is a second entry on the same thread, named by outside diameter rather than by pitch. MKK40 x 1.5P stands 22 mm high on a 65 mm outside diameter, while MKK40/85 stands 32 mm high on an 85 mm one. M30 and M35 carry a second entry as well, so check both the height and the diameter against the housing before ordering.

Choose the MKR locknut where the thread sits outside MKK's range, whether below M15 or above M130, or where an intermediate thread is needed, since MKR carries 58 sizes against MKK's 25. Choose the MKW locknut where the design wants a tall body, as MKW runs 28 to 46 mm high and can take up length a separate ring would otherwise fill. MKK remains the type to specify when the clamping force matters and the body has to stay short.

Two, on every size from M17 x 1 to M200 x 3, along with four wrench slots. Rather than adding screws as the nut grows, MA takes progressively heavier ones, reaching M12 at 56 Nm from MA135. Those are the heaviest screws in the axial series.

Choose the MKR locknut where 0.005 mm meets the drawing and the thread sits outside MA's range, below M17 or between the usual steps, as MKR carries 58 sizes against MA's 33. Choose the MKK locknut where the clamping load is better spread over four to eight screws than concentrated in two. MA is the type to specify whenever the drawing calls for 0.002 mm, and it gives the shortest body in the series as well.

A dimensioned drawing showing the thread, outside diameter, height, the tolerances that matter and the material, together with the quantity expected. Where the nut is for a spindle, include the operating speed and any residual imbalance figure the spindle builder has specified. NIKKI quotes customized locknuts against the drawing rather than against the nearest catalogue part.

In most cases, yes. Customers send us a technical drawing and we manufacture to the dimensions, tolerances and features it specifies. Where no drawing exists, send the thread size, the space available and what the nut has to do, and our engineers will tell you what else is needed before we can price the part.

NIKKI's in-house range runs to M320, covering CNC turning, threading, special machining and precision grinding on one site. Threads above the standard catalogue range are handled as custom work, and large-diameter parts are usually specified for heavy machinery where no catalogue nut reaches the thread size.

NIKKI holds maximum axial run-out to 0.002 mm on ground parts and 0.005 mm on precision-turned parts, with ISO 4H thread precision in SCM440 at HRC 28-32. Where a drawing specifies parallelism, concentricity or run-out beyond the standard grades, we review the drawing and quote against the figures on it.

Yes, and it is usually the faster and cheaper route. Altering the outside diameter, height, grinding specification or wrench interface of a standard NIKKI type keeps geometry already proven in production, so the quotation and the sample come back sooner than they would for a part drawn from nothing.

JIS SCM440 chromium-molybdenum steel (DIN 42CrMo4) at HRC 28-32 is standard, with the thread and contact surface ground to ISO 4H thread precision. JIS SUS304 stainless throughout, including locking pins and set screws, is available for food, pharmaceutical, chemical and semiconductor equipment. Other materials and hardness ranges are quoted on request.

Maximum axial run-out is 0.002 mm on grinding grade, where both the thread and the contact face are ground, and 0.005 mm on precision-turning grade. Every size is checked for thread class against gauges to ISO 4H, and thickness, inner diameter and thread run-out are measured on a universal length measuring instrument, a universal measuring microscope, and a roughness and contour instrument. Inspection records against your order are available on request rather than a generic certificate.

Yes. HSIANG KAI FU CO., LTD. holds ISO 9001:2015 for the quality management system, which covers process repeatability and record traceability. Material and substance evidence comes separately: alloy steel to ISO 683-2, an SGS test report, and a RoHS and SVHC-free certificate for assemblies shipping into the EU. All of it can be supplied with a quotation.

Use the maximum for the screw size on your part, and no more. Each screw size has one rated figure: M3 0.9 Nm, M4 2.2 Nm, M5 4.8 Nm, M6 8 Nm, M8 19 Nm, M10 36 Nm, M12 60 Nm, and M14 100 Nm.

The axial MA sizes and the single MRRA150/230 are the exception: their M12 screw is rated to 56 Nm rather than 60. The finder reads each size from its own catalogue row, so it applies that for you.

Per screw. A NIKKI nut carries three, four, six or eight screws depending on the size, and each one takes the rated torque. The finder shows the screw count next to the figure so you can see what the part needs.

Clean and dry the shaft and nut, oil the threads, then tighten the screws to the rated figure with a torque wrench. Oiling is part of the method, because tightening torque and the clamp force it produces are linked through friction, which is what the test in ISO 16047 measures. That is why NIKKI publishes these as reference figures rather than exact settings, and why a dry or dirty thread changes the result.

No. NIKKI publishes a rated maximum per screw, not a torque derived from a target preload, so neither the finder nor this page converts a required axial force into a screw torque. If you need that, send the load, thread size and application to NIKKI through an RFQ and their engineers will advise.

Yes, from the thread size and pitch, height, outside diameter, and locking method. The one detail worth supplying is the precision grade of your current part, since many competitor codes don't carry it. NIKKI's own codes do: where a series comes in both grades, a code carrying Z is the precision-turned version at 0.005 mm run-out and the code without it is ground to 0.002 mm, so MR and MRZ are the same nut in two finishes. The locknut cross-reference tool will place most competitor part numbers, or send us the code with the shaft drawing.

From NIKKI's published static-axial-load data: the formula F = A·Sh·n and the reference curve in the catalogue's technical information, where F is axial load, A the thread area, Sh the allowed shearing stress (with a safety factor of 4), and n the number of effective threads. The tool returns the catalogue reference for each size.

No. This is the static load the thread engagement can carry — a thread-capacity figure. It is not the axial clamping (holding) force the set or clamping screws generate; NIKKI does not publish a clamping-force figure. If you need holding force for your application, send the details to our team.

Treat it as a reference for sizing and comparison, not a final rating. It assumes static load and even thread engagement, and the catalogue marks it "for reference only." For a verified figure at your load, speed and mounting, contact us and our engineers will advise.

NIKKI's published curve covers M20 to M200. The tool still returns a figure for smaller and larger threads by extending the same slope, but treat those as estimates and confirm them with our team.