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Lock Washer

Safety Nut

Bob-Lock Safety Nut



The object of Best on Bolt is to provide a secure lock against loosening. The well-tried Bob-Lock wedge lock washers from Best-On-Bolt fulfil all usual demands on a vibration-resistant locking element. The latest development from Best on Bolt, based on the wedge lock principle, is a high performance Safety Nut, which meets the following requirements:
  • The Bob-Lock Safety Nut secures the bolt with highest reliability without any damage to the surface of the work piece respectively to the bolt and the nut as in the case with tooth or wedge lock washers.

  • The bolt is secured with highest reliability independent from any settlement in the bolted joint.

  • The lock is performed solely on the nut and there is no action on the bolt head. This feature facilitates considerably the assembling and enables it to be used with the stud bolts.

  • It is possible to add free spinning washers at the bolt head and the nut which serves as a surface protection and better pressure distribution without cancelling the effectiveness of the securing facility. This loss of security happens to all other braced locking washers.

  • We use the torque values of the bolt manufacturers to achieve the necessary clamp load without restriction because our design has no rough surface and therefore no correction for increased friction has to be taken into consideration as in the case for tooth washers and wedge lock washers.

  • Also of importance is that the Bob-Lock Safety Nut can be reused a high number of times without wear or loss of effectiveness.

  • Another feature is that the thread of bolt and nut can be lubricated with no reduction in the locking effectiveness.

  • The Bob-Lock Safety Nut requires no change whatsoever to the bolt.

  • The new securing facility can even be mounted behind the assembled standard nut.

  • The width across flats and the required wrench size are the same as is for the standard nut.

  • Most important is that the assembly of the Bob-Lock Safety Nut is easy and fail safe.



Pic 1-2: Components of the safety nut


Pic 3-4: Washer-packet and assembled safety nut




Fig. 1: Sectional drawing / exploded drawing

Fig. 2: View of the assembled nut

Fig. 3: Side view of the washer-packet

Fig. 4: View from above/below on the middle washer

Fig. 5: Outer washer - view from below

Fig. 6: Outer washer - view from above

Fig. 7: Non-operative bolted joint

Fig. 8: Bolted joint under dynamic load

Fig. 9: Sectional drawing of a washer-packet with cover

Fig. 10: Version with cover cap


Function Description of the Bob-Lock Safety Nut

The new Bob-Lock Safety Nut for the securing of bolted joints against loosening consists of a 3-disc pack, set into a nut, and a short threaded pin as a lock bolt, which presses the 3-disc pack to the shaft’s end of the secured bolt. The three discs are wedge lock washers, which are comprised by a central ring. The central wedge lock washer has tabs, which are situated into corresponding grooves of the nut. The grooves are not end-to-end, so the 3-disc pack cannot fall through.
The nut can be tightened with the original torque value and only afterwards follows the contact between the outer washer and the shaft’s end, so no damage of the work piece and no loss of clamp load due to raised friction results. The cams of the wedge lock washers have an angle, which is higher than the angle of the pitch. When the nut and/or the lock bolt starts loosening, two washers distort against each other and as a result of the wedge design, they shift axial and so create a self-locking effect. The security effect of the safety nut concerns both, the nut and the screw, without the need of any additional measure on the bolt head and it functions also on a free spinning washer.
The Bob-Lock Safety Nut has the same radial measurements as a standard nut and includes in its height a tolerance sector for various screw lengths (5-10 mm, depending on the standard lengths of the bolts). Present bolts can retain, and the safety nut can also be mounted behind a not disassembled standard nut.
The Bob-Lock Safety Nut will be delivered as a one-piece element with pre-assembled 3-disc pack and lock bolt. The standard quality of the nut is 10, the coating is Delta Protekt. If desired, a coloured cover cap made of plastics can be added as a security signal.


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