APPENDIX B - LOCKWIRE
The following items must be firmly attached in a positive manner with lock wire (safety wire). The lock wire must be new, not reused, and of the stainless steel type, not copper:
- Lock wiring is the securing together of two or more parts with a wire, which shall be installed in such a manner that an additional tightening of the wire will counteract any tendency for a part to loosen.
- For general-purpose lock wiring, use the preferred sizes of .032”. Use smaller diameter wire where parts are too small to permit a hole diameter to accommodate the preferred size, or where space limitations preclude the use of the preferred size. Larger sizes are used where stronger wire is required.
- All lock wire must be stainless steel.
- The common method of installing lock wire shall consist of two strands of wire twisted together (double twist). One twist is two wires turned through 180 degrees or half a complete turn. The single strand method of lock wiring may be used for some applications, such as in a closely spaced, closed geometrical pattern (triangle, square, rectangle, circle, etc.), or parts in electrical systems.
- The maximum span of lock wire between tension points shall be 6 inches.
- Where multiple groups are lock wired by either the double twist or the single strand method, the maximum number in a series shall be determined by the number of units that can be lock wired by a 24 inch length of wire.
- Caution must be exercised during the twisting operation to keep the wire tight without over-stressing. Abrasions caused by commercially available wire twisting pliers shall be acceptable but nicks, kinks, and other damage to the wire are not.
- Lock wire shall not be installed in such a manner as to cause the wire to be subjected to chafing, fatigue through vibration, or additional tension other than the tension imposed on the wire to prevent loosening. In the event that no wire hole is provided, wiring should be to a convenient neighbouring part in a manner so as not to interfere with the function of the parts. Hose and electrical coupling nuts shall be wired in the same manner as tube coupling nuts. Check the units to be lock wired to make sure that they have been correctly torque. Under torque or over-torque to obtain proper alignment of the holes is not advisable. It is impossible to obtain a proper alignment within the specified torque limits, back off the unit and try it again or select another unit.
- In adjacent units, it is desirable that the holes be in approximately the same relationship to each other, thus the lock wire will have a tendency to pull the unit clockwise (for right handed threads). This should be reversed for left-hand thread.
- Where lock wire is used to secure a castellated nut on a threaded item, selection of locking hole diameter for the item shall be based on cotter pin requirements.
- Lock wire outline section courtesy of AAMRR: American Association of Motorcycle Road Racers.
There are a few examples following, and many other various examples of lock wiring can be found on the EMRA web site, http://www.emra.ca in the Tech section.