FUJI Fine U-Nuts
Reusable, one‑piece locking nuts with a friction‑ring design
Fine U‑Nut Features & Benefits
Fine U‑Nuts combine a nut and friction ring in one reusable ball‑bearing locknut. Tightening causes the ring to flex along the shaft thread, generating torque that locks the nut and eliminates the need for lock washers or keyway machining, saving time and cost. Lightweight and balanced, Fine U‑Nuts suit high‑speed, vibration‑prone applications and can be reused with minimal torque loss.
- Reusability: Fuji bearing lock nuts may be re-used with very little prevailing torque decline.
- Simple fastening: Fine adjustment is possible from any position, and torque management is easy.
- Simple and time-saving installation : Eliminates the need for toothed lock washers and the keyway machining of shafts.
- Balance: Improves rotational balance of the shaft.
- Weight reduction: Allows for the use of hollow shafts that are thinner than normal.
- Cost reduction: Achieves a total cost reduction by eliminating the need for processing, parts, and technology that were previously required
- Dedicated tools in a range of sizes, from M10 to M100, are available
How the Fine U‑Nut Works
When “FINE U-NUT” is screwed onto a shaft, the friction ring comes into contact with the shaft thread. As the nut is tightened further, the friction ring begins to bend along with the screw thread and presses against the shaft screw threads.A spring effect produced by the friction ring (P), along with a reactionary force that pushes against the screw flank surface (P’), generates prevailing torque (frictional torque) and demonstrates the locking function.
Fine U‑Nut vs. Conventional Locknuts
- Consists of 3 basic parts
- No need for a lock washer
- Just insert to fasten
- No need to for specialist machining of keyways into shaft
Conventional Product
- Consists of 4 basic parts.
- A toothed lock washer and keyway machining are required.
Basic Specification
Dimentional Charts
Prevailing Torque
FINE U-NUT Dimensional Chart
| Steel friction ring | 270°ring |
|---|---|
| Thread accuracy | JIS6H (JIS Class 2) Face runout (maximum): 0.05 mm (M8 to M50) Face runout (maximum): 0.07 mm (M55 to M120) Face runout (maximum): 0.10 mm (M125 to M150) |
| Sizes | M 8 to M100 (SS Series) M10 to M150 (SC Series) M10 to M100 (SUS Series) *Pitch: Fine thread |
| Shapes | Grooved round nut *Other special shapes |
| Materials | SS400 or equivalent, S45C (thermal refined), SUS304 or equivalent |
Installation Instructions
1
Thread the bearing through the shaft thread. Check that the tip of the shaft thread has been chamfered (C = 1 pitch or equivalent) before applying lubricant. If the hardness of the shaft thread is low, use a lubricant with especially high lubricating performance.
2
Thread the bearing through the shaft thread. Check that the tip of the shaft thread has been chamfered (C = 1 pitch or equivalent) before applying lubricant. If the hardness of the shaft thread is low, use a lubricant with especially high lubricating performance.
3
Use a tightening tool made especially for the FINE U-NUT.
*An impact wrench cannot be used.
4
Push down on the axis portion of the ratchet handle and gently turn the ratchet to tighten.
*The nut cannot be screwed on from the friction ring side.
5
Check that the inner ring of the bearing is in complete contact with the seat surface of the FINE U-NUT, and that at least two full shaft threads come out of the friction ring.
When removing the nut, use a tightening tool to unscrew it until the friction ring is separated from the tip of the threaded portion of the shaft.
6
*A hook wrench can also used to remove the nut.
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