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close this bookThreaded Joints - Course: Techniques of Fitting and Assembling Component Parts to Produce Simple Units. Trainees' Handbook of Lessons
View the document(introduction...)
View the documentPreliminary Remarks
View the documentHints on Labour Safety
View the document1. Purpose of Threaded Joints
View the document2. Selected Types of Bolts and Screws
View the document3. Selected Types of Nuts
View the document4. Selected Types of Locking Devices for Bolts and Screws
View the document5. Selected Types of Washers
View the document6. Types of Threaded Joints
View the document7. Stresses in Threaded Joint
View the document8. Tools
View the document9. The Technological Steps of Making Threaded Joints
View the document10. Undoing Threaded Joints

4. Selected Types of Locking Devices for Bolts and Screws

Locking devices can be acting positively, non-positively or by the retention of self-substance.

Locking devices, particularly cotter pins, spring rings and toothed washers, are used only once.

Use new, unused locking devices when re-assembling parts which have been dismantled. Locking devices, once used, will deform permanently and not be safe to use another time.

Non-positive locking devices

These are available mainly as spring lock washers and toothed washers. They maintain a slight tension between the bolt, or nut, and the component to which they are fastened.

The sharp edges on the spring lock washers and toothed lock washers have a “seizing” effect on the component tightened in the joint, thus preventing it from coming loose accidentally.

An additional locking effect can be obtained on bolts with a long, projecting shank by screwing a counternut on the projecting shank. Both nuts must be screwed sufficiently tight. The friction on the thread flanks prevents the nuts from coming loose.


Figure 11. Non-positive locking by

1 spring ring, 2 toothed washer, 3 counter nut, 4 spring lock washer

Positive locking devices

These are available mainly as locking plates, retaining rings and crown nuts with split pins. They are used primarily with hexagon head screws and where their shape prevents the joint from coming loose.

Locking plates and retaining rings are provided with tangs or lugs, which are fastened to the component in the joint and the connecting part by blows with a hammer. When crown nuts are used, a hole must be drilled through the threaded portion, which takes up the cotter pin, after nut has been tightened.


Figure 12. Positive locking by

1 crown nut with split pin, 2 locking plate with tang

Locking by retention of self-substance

The locking effect is achieved by the application of paint, varnish or paste. Used primarily on electrical assemblies and in precision instruments. Where the forces acting on the joint are slight, the locking effect is sufficiently strong and provides protection against tampering.


Figure 13. Locking by retention of plaint

1 on the bolt head at a blind bore, 2 on the nut at a through bore

Identify elements of locking devices which must be used once only.
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Suggest an effective way of locking with the shank of the bolt projecting beyond the nut.
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