Reason for choosing FUJILOK U-NUT

U-NUT冨士精密

U-NUT

FUJILOK U-NUT has passed over 50 years since the birth. It is a groundbreaking Locknut manufactured by Fuji Seimitsu as the first in the industry to feature a metal ring locking function. It's brought a revolution from which it is unavoidable loosening in the bolts and nuts industry.
FUJILOK U-NUT is now the highly regarded as the first name in Locknuts across all industries such as railways, bridges, automobiles, motorcycles and industrial machines.


TOP ProductsWhat is FUJILOK U-NUTReason for choosing FUJILOK U-NUT

"Metal ring locking function" for the first in the industry

The FUJILOK U-NUT is consisted of a nut and friction ring (special spring). The friction ring is integrated with the top face of the nut by crimping.
Nowadays, as a substitute for anti-loosening nuts, "FUJILOK U-NUT", which is widely used in the industry, are used in all industries from steel structures such as railways and bridges to cars, motorcycles, and industrial machinery.

メタルリングゆるみ止め機能

"Locking effect" by Friction Ring

FUJILOK U-NUT is tightened on a bolt, the friction ring touches the bolt screw threads.
The friction ring then begins to bend along with the screw threads and press against the bolt screw threads.
Stress produced through a spring effect and Prevailing Torque (friction torque) caused by a reaction force that presses against the bolt thread are produced.
This will be locking operation.

ゆるみ止め効果1
ゆるみ止め効果2
ゆるみ止め効果3
ゆるみ止め効果4

Reason for choosing FUJILOK U-NUT

  • Easy to install

    取り付け簡単

    The same as general nuts, "FUJILOK U-NUT" is easy to install.

  • Heat-resistant

    熱に強い

    As it is made of metal, it is not affected by heat as compared with nylon insert nuts.

  • Prevents nuts from quickly coming off

    早期脱落防止

    Quick coming off can be prevented even if axial force drops. In addition, it is effective even in the middle position of the bolt.

  • Variety of shapes

    形状多種

    Various shapes are available, such as Cap Type U-NUT and Weld Type U-NUT.

  • Variety of size

    サイズが豊富

    Thread sizes are from M3 up to M115. You can find your requested size.

  • Special order is available

    オーダー作成可能

    Production with special shape is also available.


Features

・ Provides a stable locking function.

・ Prevents nuts from quickly coming off even if the tightening force is lowered.

・ It is all metal products and is excellent in heat resistance and cold resistance.

・ Easy tightening prevents installation mistakes.

・ Can be reused.
Stainless Spring Steel Friction Ring

60° 3-wing ring structure (up to M6),
90° 2-wing ring structure (M8 and above)
Accuracy Thread accuracy: JIS6H (Old JIS class 2)

The FUJILOK U-NUT consists of a Nut and Friction Ring (specialized spring). The Friction Ring is secured to and integrated with the top face of the nut by crimping. The Friction Ring touches the bolt screw threads, and stress (P) is produced through a spring effect when the nut is tightened as shown on the left. Along with a reaction force (P'), a frictional torque (prevailing torque) that presses against the bolt screw threads and prevents free rotation is produced.

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Prevailing torque is the frictional torque that is produced by the Friction Ring acting on the bolt screw threads. (The values of following graphs are when lubricant is used.)

 

> U-NUT's Tightening torque

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Vertical Axis Vibration Test

Test Condition

Sample size

 M12×1.75

Material of sample nut ・ bolt

SS400 or equivalent

Axial tension for fastening

 17150N [1750kgf]

 

● Specification of Yunker Type Thread Loosening Testing Machine

Frequency of vibration plate 200c.p.m
Displacement of vibration ±0.5mm
Vibration time 5 min.

 

Vertical Axis Vibration Test

Test Condition

Sample size

 M12×1.75

Material of sample nut ・ bolt

SS400 or equivalent

Axial tension for fastening

 17150N [1750kgf]

● Specification of NAS Conforming High Speed Thread Looseness Test Machine

Frequency 1780c.p.m
Excitation stroke 11mm
Impact stroke 19mm
Vibrating acceleration of excitation table 19.5G

● Test Result

Sample nut Frequency Vibration time
U-NUT 30000 cycles 16' 51"
No problem
Double nut 4450 cycles 2' 30"
Came off
Ordinary nut + Washer 1335 cycles 45 sec.
Came off

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  1. Insert a bolt to a tightening member. Use bolts with a chamfered tip with thread accuracy of ISO 6g.


  2. Manually screw the nut on until the friction ring touches the tip of the thread portion of the bolt. ※ The nut cannot be installed from the friction ring side.


  3. Tighten the nut with a tightening tool such as a wrench. Please refer to the reference tightening torque table for tightening torque. If use under severe conditions or with low axial tension, consult us.


  4. Check that at least two full bolt threads protrude beyond the friction ring. When removing, unscrew the nut with a tightening tool such as a wrench until the friction ring is detached from the tip the threaded portion of the bolt. After that, unscrew the nut manually.

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This product is used for especially safety position. Observe strictly the following items when using.

  • Use bolts with a chamfered tip with ISO 6g (Class 2) thread accuracy.

  • Please refer to the tightening torque table when tightening.

  • Use lubricant where problems such as scorching or seizing may occur during installation and remove of a nut.

  • For full locking, ensure that two full bolt threads protrude beyond the friction ring at the top of the FUJILOK U-NUT.

  • When welding a nut, pay attention to the effect of heat and splattering on the friction ring and thread areas.

  • Consult us before using the nut if the bolt thread is mchined with key ways or pin holes.

  • The nut cannot be installed from the friction ring side.

  • High speed rotation impact wrench cannot be used.

  • Stop using the nut if excessive deformation or another fault is found on the Friction Ring and the clamp.

  • If use under severe conditions or with low axial tension, consult us.