How BF Locks on the 30° Thread Flank
BF locks through a brass pad rather than through the set screw itself. Each screw drives the pad onto the shaft's thread flank at a 30° radial angle, spreading the load along the flank instead of denting the thread crest. No slot is cut in the shaft, so the section stays intact and the nut can be taken off and refitted.
The full explanation is on the 30° Flank Locking Series page.
Straight Outer Profile
Hook wrench reaches a recessed nut
No Thrust Washer or Keyway
Fewer parts, simpler assembly
Ground Contact Surface and Thread
Maximum axial run-out 0.002 mm
3 or 6 Set Screws Per Nut
M5 to M14. 4.8 to 100 Nm max
Where BF Locknuts Are Used
Bearing Retention in Counterbored and Recessed Housings
Gearbox and Reducer Output Shafts
Rolls and Conveyor Drums
Large-Diameter Assemblies From M180 Up, Where the Set Screws Step Up to M12
Find Your Size(M15 to M260)
Filter DIN flange locknuts by shaft diameter, height, or pitch.
Products in this 30° Flank Locking Series
Grinding
MF
Grinding
Hook wrench · nut exposed
M12×1 to M260×4 · h 14–36 mm
MF is the original 30° flank locknut, ground to 0.002 mm. Use it where the nut sits clear of the housing and a hook wrench has room to work.
BF
Grinding
Hook wrench · nut recessed
M15×1 to M260×4 · h 14–40 mm
BF has a straight outer profile that stays reachable when the housing covers part of the nut, so a hook wrench still has a square surface to seat against. Same locking as MF.
TMF
Grinding
Pin wrench
M20×1 to M200×3 · h 18–32 mm
TMF is driven through holes in its face with a pin wrench (pin spanner in UK and EU practice). It is ground only, with no precision-turned equivalent.
Precision turning
MFZ
Turning
Hook wrench · nut exposed
M12×1 to M260×4 · h 14–36 mm
MFZ is the precision-turned version of MF, with the same envelope and hook-wrench profile at 0.005 mm run-out instead of 0.002 mm.
BFZ
Turning
Hook wrench · nut recessed
M15×1 to M260×4 · h 14–40 mm
BFZ is the precision-turned version of BF, with the same straight profile and hook-wrench access at 0.005 mm run-out.
SFZ
Turning
Open-end wrench · two flats, to M75
M10×0.75 to M200×3 · h 14–32 mm
SFZ has two parallel flats for an ordinary open-end wrench, up to M75 only. It is the only type down to M10 × 0.75, and the type used most in Japan.
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Questions About the BF Locknut
The BF is the straight-profile locknut in NIKKI's 30° Flank Locking Series, in metric threads from M15 x 1 to M260 x 4 with 0.002 mm maximum axial run-out. The questions below are the ones buyers ask before a first order.
Contact UsThe maximum axial run-out of a BF locknut is 0.002 mm. We finish both the thread and the contact surface by high-precision grinding, which is what holds the run-out to this level. The precision-turned BFZ is the same nut at 0.005 mm.
BF and MF lock identically, with the same 30° flank and the same 0.002 mm maximum run-out in SCM440. BF has the straight outer profile, so a hook wrench still seats when the housing covers part of the nut. MF is the choice where the nut sits clear, and it goes one size smaller, to M12 x 1.
Each BF size lists a catalog maximum per screw in the dimension table, from 4.8 Nm on the M5 screws of BF15 up to 100 Nm on the M14 screws of BF260. Tighten gradually and alternately rather than one screw fully first.
Add L to the order code for a left-hand thread (BF30x1.5P-L) or U for an inch thread (BF30-U18). Standard right-hand metric versions are ordered by the plain name, for example BF30x1.5P.
BFZ is the precision-turned version of BF, in the same envelope and the same profile, at 0.005 mm maximum axial run-out instead of 0.002 mm and at lower cost. Specify BFZ where the drawing tolerance allows 0.005 mm, and BF where it doesn't.
No. BF 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.