FUJILOK U-nut

Features

Fastening function: Demonstrates stable locking function
Dropout prevention: Prevents premature detachment even if the tightening force is lowered
Reusability: Fuji bearing lock nuts U-nut may be re-used with very little prevailing torque decline.
Simple fastening: Easy tightening with no need for skilled techniques or specialized tools
Simplex parts: It demonstrates a locking effect by itself, making parts management easy and preventing installation errors
Heat and cold resistance: An all-metal product with excellent resistant to heat and cold

Applicable Markets

Lineup

Structure & Function

The FUJILOK U-NUT consists of a nut and friction ring (specialized ring).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 effetct when the nut is tightened as shown on the left. Along with a reaction force (P’), a frictional torque (prevailing torque=P) that presses against the bolt screw threads is produced.

Steel friction ring	60° 3-wing ring (up to M6) 90° 2-wing ring (M8 and above)
Thread accuracy	JIS6H(JIS Class2),formerly JIS Class2, JIS2B
Sizes	M3 – M115　Pitch: Coarse thread and fine thread W3/16-24 – W2″-4.5 NC#10-24 – NC1″1/2-6 NF#10-32 – NF1″1/2-12 Other special sizes
Shapes	FUJILOK U-NUT Single Chamfer(Type 1), Double Chamfer (Type 2), Thin Type (Type 3), Small Type U-NUT, Flange Type U-NUT, Cap Type U-NUT, Weld Type U-NUT.
Materials	SS400 or equivalent, S45C thermal refined or equivalent, SUS304 or equivalent, SCM435 (thermal refined), titanium, SUS316L, brass (BSBM) *Other special materials

Performance of the prevailing torque and reusability

Prevailing torque is produced by the spring effect when the friction ring touches the bolt threads.

Sample

M12 × 1.75 SS400 equivalent non-plating
Maximum Installation torque		Minimum removal torque
1cycle	10cycle	1cycle	10cycle
1.20	0.75	0.70	0.50

[N・m]

*Via in-house testing

Even re-used 10 times, the prevailing torque shows only a slight decrease.

Test Condition

Bolt material	Alloy steel (SCM435)
Thread accuracy	ISO6g (JIS6g)
Surface treatment	plain (nut and bolt)
Lubricant	penetrating lubricant

Junker Type Thread Looseness Test (according to DIN 65151)

This test repeatedly applies amplitude and impact in a direction vertical to the axis of the bolts and nuts that are assembled in a vibration plate in order to examine the reduced axial tension of the fastener and judge the locking performance.

Test Condition

Sample size	M12×1.75
Material of the sample nut, bolt	SS400 or equivalent
Axial tension for fastening	17,150N{1,750kgf}

Specification of the Junker Type Thread Loosening Testing Machine

Frequency	1,278c.p.m.
Excitation stroke	11mm
Impact stroke	10mm
Vibration acceleration of the excitation table	10G
Excitation time	60 min.
Direction of impact	Bolt axial direction

Test Result

Vertical Axis Vibration Test video

NAS Conforming High Speed Thread Looseness Test (according to National Aerospace Standard NAS3350)

This test repeatedly applies shocks in a direction vertical to the axis of the bolts and nuts that are assembled a vibration barrel in order to examine whether or not loosening occurs and judge the locking performance.

Test Condition

Sample size	M12×1.75
Material of the sample nut, bolt	SS400 or equivalent
Axial tension for fastening	17,150N{1,750kgf}

Yield point of Bolt σy：314N/mm²｛32kgf/mm²}

Specification of NAS Conforming High Speed Thread Loosening Testing Machine

Frequency	1,780 c.p.m.
Excitation stroke	11mm
Impact stroke	19mm
Vibration acceleration of the excitation table	19.5G

Test Result

Sample size	Frequency	Vibration time
FUJILOK U-NUT	30,000cycles	16′ 51″
FUJILOK U-NUT	No problem
Double nut	4,450cycles	2′ 30″
Double nut	Failed
Ordinary nut + Washer	1,335cycles	45 sec.
Ordinary nut + Washer	Failed

Vertical Axis Vibration Impact Test video

Installation Instructions

1

Thread the bolt through the fastening member. Check that the bolt has been chamfered at the tip of the threaded area with a thread accuracy of JIS6g (Class 2). If there is risk of galling or sticking, use lubricant.

2

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

3

Tighten the nut with a tool such as a wrench/impact wrench. Please refer to the reference tightening torque chart for the tightening torque. Please contact us if you will be using the FUJILOK U-NUT under severe conditions or with low axial force.

4

Check that at least two full bolt threads protrude beyond the friction ring. When removing the nut, use a wrench or other such tool to unscrew the nut until the friction ring is separated from the tip of the threaded portion of the bolt.

1

Thread the bolt through the fastening member. Check that the bolt has been chamfered at the tip of the threaded area with a thread accuracy of JIS6g (Class 2). If there is risk of galling or sticking, use lubricant.

2

Manually tighten the nut until the friction ring touches the tip of the thread portion of the bolt.

3

Tighten the nut on at low speed from directly above. Working while the bolt is slanted or installing the nut at high rotating speeds may cause galling.