How SRZ Locks at 90° to the Shaft
SRZ locks through a brass pad rather than through the set screw itself. Each of the two 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.
Same Dimensions as SR
Ground and turned grades interchange
Turned Grade at 0.005 mm
Below the price of the ground SR
Four Hook Slots
More places for the wrench to seat
Two Set Screws Per Nut
M4 to M12. 2.2 to 60 Nm max
Where SRZ Locknuts Are Used
Volume Builds Where the Drawing Allows 0.005 mm and the Budget Will Not Carry the Ground Grade
Large Threads Above M130 x 2, Where the M12 Screws at 60 Nm Carry More Clamping Load Than the Three-Screw Types Manage
Bearing and Gear Retention in Compact Gearboxes and Reducers
Installations Where the Housing Leaves the Wrench an Awkward Approach, and a Fourth Slot Decides Whether the Nut Can Be Turned at All
Assemblies Where a Keyway Would Take Out Section the Shaft Cannot Spare
Find Your Size(M6 to M200)
Filter SRZ locknuts by shaft diameter, height, or pitch.
Products in this Radial Locking Series
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 SRZ Locknut
The SRZ is the precision-turned two-screw 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 SRZ 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 SR locknut is the same nut at 0.002 mm.
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.
Each SRZ size lists a catalog maximum per screw in the dimension table, from 2.2 Nm on the M4 screws of SRZ6 up to 60 Nm on the M12 screws fitted from SRZ135. Every size carries two screws. Tighten the pair gradually and alternately rather than one screw fully first.
Add L to the order code for a left-hand thread (SRZ30x1.5P-L) or U for an inch thread (SRZ30-U18). Standard right-hand metric versions are ordered by the plain name, for example SRZ30x1.5P.
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.
No. SRZ 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.