How MRS Locks at 90° to the Shaft
MRS locks through a soft pin rather than through the set screw itself. Each of the three screws enters through the outside diameter, meets the shaft at 90°, and drives its pin onto the thread flank, spreading the load along the flank instead of denting the crest. Where the rest of the series uses brass for that pin, MRS uses stainless, which is what keeps the whole nut to one material.
The full explanation of the locking principle is on the Radial Locking Series page.
JIS SUS304 Throughout
Stainless pin and set screws included
Same Dimensions as MRZ
Fits a housing drawn for the steel nut
Maximum Axial Run-Out 0.005 mm
ISO 4H thread precision
Three Set Screws Per Nut
M4 to M6. 2.2 to 8 Nm max
Where MRS Locknuts Are Used
Food and Beverage Processing Equipment Washed Down Between Shifts
Pharmaceutical Production and Clean-Room Machinery
Chemical Plant, Where a Plated or Blacked Steel Nut Gives Up Early
Semiconductor Equipment
Any Assembly Where a Brass Pad Would Be the One Non-Stainless Part on an Otherwise Stainless Shaft
Shafts That Can't Take a Keyway
MRS Specifications
Please enter your specifications below to find the right product for your project.
Machined from JIS SUS304 stainless steel, threads to class 4H per ISO 965-1. SUS304 is one of the JIS grades covered by ISO 15510, which sets out stainless compositions across the ISO, ASTM, EN and JIS systems.
All dimensions in mm. The d1 diameter is listed from MRS25 x 1.5 upward. Every size takes three set screws.
Find Your Size(M6 to M50)
Filter MRS locknuts by shaft thread, pitch, or height.
Products in this Radial Locking Series
All seven lock the same way, with set screws at 90° driving a pad onto the thread flank, most in a body shorter than the 30° flank equivalent. What differs is the machining grade, the wrench the nut takes, the number of set screws carrying the clamping load, and in two cases the material and the duty the type is built for.
Grinding
MR
Grinding
Hook wrench · three set screws
M6×0.5 to M260×4 · h 8–30 mm
MR is the general-purpose radial locknut, ground to 0.002 mm, with three set screws at 120° and the widest range in the series. Use it where the drawing calls for the ground grade, and wherever the thread runs above M200 × 3.
SR
Grinding
Hook wrench · two set screws
M6×0.5 to M200×3 · h 8–32 mm
SR is the two-screw ground type, with four hook slots at every size where MR has three hook slots below M105 and six above, and heavier set screws at the top of the range, M12 at 60 Nm from SR135 where MR stays at M10 and 36 Nm.
MRRA
Grinding
Hook wrench · two set screws
M15×1 to M150×2 · h 20–42 mm
MRRA is the type for high radial torque, taller and heavier in the body than the rest of the series. Sizes from M20 to M50 are offered in two outside diameters, so the same shaft thread can carry a much larger contact face. Ground only.
Precision turning
MRZ
Turning
Hook wrench · three set screws
M6×0.5 to M200×3 · h 8–30 mm
MRZ is the precision-turned version of MR at 0.005 mm, matching it size for size up to M200 × 3 and adding fine-pitch rows at M55, M60, M65, M70 and M75 that MR does not carry.
SRZ
Turning
Hook wrench · two set screws
M6×0.5 to M200×3 · h 8–32 mm
SRZ is the precision-turned version of SR, with the same envelope, the same four hook slots and the same set screws at 0.005 mm run-out.
MRN
Turning
Open-end wrench · two flats
M5×0.5 to M40×1.5 · h 5–25 mm
MRN is drawn for light-duty transmission work and takes an ordinary open-end wrench on two flats. It reaches M5 × 0.5 at a 12.5 mm outside diameter, the smallest locknut NIKKI makes.
MRS
Turning
Hook wrench · three set screws
M6×0.5 to M50×1.5 · h 8–14 mm
MRS is fully SUS304 stainless, locking pin and set screws included, for food, pharmaceutical, chemical and semiconductor equipment. Dimensionally it matches MRZ across its range.
Tell Us What You Need. We'll Find the Locknut.
Give us the locknut code you use now and we'll find the NIKKI equivalent.
Describe the job, thread size, space, load, and we'll point you to the right NIKKI series.
Questions About the MRS Locknut
The MRS is the stainless locknut in NIKKI's Radial Locking Series, in JIS SUS304 from M6 x 0.5 to M50 x 1.5 with 0.005 mm maximum axial run-out. The questions below are the ones buyers ask before a first order.
Contact UsMRS 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.
The maximum axial run-out of an MRS locknut is 0.005 mm, the same figure as the precision-turned steel types in the series. Where a drawing calls for 0.002 mm, no stainless option exists; the ground grades are all SCM440.
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.
Each MRS size lists a catalog maximum per screw in the dimension table, 2.2 Nm on the M4 screws of MRS06 to MRS15, 4.8 Nm on the M5 screws of MRS17 and MRS20, and 8 Nm on the M6 screws from MRS25. Every size carries three screws at 120°. Tighten gradually and alternately rather than one screw fully first.
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.
No. MRS locks between the set screws, the stainless pins, and the thread flank, all inside the nut, so neither a thrust washer nor a shaft keyway is required. Nothing else goes on the shaft, and the nut is reusable if handled properly.