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.
"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.
"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.
Reason for choosing FUJILOK U-NUT
Easy to install
The same as general nuts, "FUJILOK U-NUT" is easy to install.
As it is made of metal, it is not affected by heat as compared with nylon insert nuts.
Prevents nuts from quickly coming off
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
Various shapes are available, such as Cap Type U-NUT and Weld Type U-NUT.
Variety of size
Thread sizes are from M3 up to M115. You can find your requested size.
Special order is available
Production with special shape is also available.
・ 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)
Thread accuracy: JIS6H (Old JIS class 2)
Structure & Function
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.
Insert a bolt to a tightening member. Use bolts with a chamfered tip with thread accuracy of ISO 6g.
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.
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.
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.