How MRZ Locks at 90° to the Shaft
MRZ locks through a brass pad 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 pad onto the thread flank, spreading the load along the flank instead of denting the crest. A screw sitting square to the axis needs only its own diameter of height in the body, which is where the shorter nut comes from.
The full explanation is on the Radial Locking Series page.
Turned Grade at 0.005 mm
Below the price of the ground MR
No Thrust Washer or Keyway
Fewer parts, simpler assembly
Pitch Options MR Does Not List
Both 1.5 and 2.0 at M55 to M75
Three Set Screws Per Nut
M4 to M10. 2.2 to 36 Nm max
Where MRZ Locknuts Are Used
Volume Builds Where the Drawing Allows 0.005 mm and the Budget Will Not Carry the Ground Grade
Bearing and Gear Retention in Compact Gearboxes and Reducers
Impeller and Rotor Retention on Pumps, Fans and Blowers
Shafts Needing a 1.5 Pitch Between M55 and M75, Which MR Does Not List
Assemblies Where a Keyway Would Take Out Section the Shaft Cannot Spare
Find Your Size(M6 to M200)
Filter MRZ 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.
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Questions About the MRZ Locknut
The MRZ is the precision-turned locknut in NIKKI's Radial Locking Series, in metric threads from M6 x 0.5 to M200 x 3 with 0.005 mm maximum axial run-out. The questions below are the ones buyers ask before a first order.
Contact UsThe maximum axial run-out of an MRZ locknut is 0.005 mm. NIKKI finishes both the thread and the contact surface by precision turning, which is what sets the run-out at this level and keeps the cost below the ground grade. The ground MR is the same locking principle at 0.002 mm.
Both lock the same way in SCM440 at HRC 28-32, with three set screws at 90° to the shaft. MRZ is precision turned to 0.005 mm maximum axial run-out and costs less; MR is ground to 0.002 mm. 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. MRZ stops at M200 x 3, where MR continues to M260 x 4.
Each MRZ size lists a catalog maximum per screw in the dimension table, from 2.2 Nm on the M4 screws of MRZ6 up to 36 Nm on the M10 screws fitted from MRZ140. MRZ carries three set screws at every size, with three hook slots up to MRZ100 x 2 and six from MRZ105 x 2 upward. Tighten gradually and alternately rather than one screw fully first.
Add L to the order code for a left-hand thread (MRZ25x1.5P-L) or U for an inch thread (MRZ25-U20). Standard right-hand metric versions are ordered by the plain name, for example MRZ25x1.5P.
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.
No. MRZ locks between the set screws, the brass pads, 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.