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Welding, Bonding & Fastener engineering FAQ

Fastener Information Sources

What about Safety Wire? by MintJulep
Posted: 6 Jun 09

Many people see safety wire used on airplanes, and thus think that it must be the best way to prevent fasteners from loosening.  Not so.  Here is what a bunch of literature says:


Fastener Design Manual; NASA Reference Publication 1228
    Although lockwiring is a laborious method of preventing bolt or nut rotation, it is still used in critical applications, particularly in the aerospace field.


Acceptable Methods, Techniques and Practices – Aircraft Inspection and Repair; FAA Advisory Circular AC43.13-1B
    These practicesare not a means of obtaining or maintaining
torque, rather a safety device to prevent the
disengagement of screws, nuts, bolts, snap
rings, oil caps, drain cocks, valves, and parts.


Bickford, John H., 1981 An Introduction to the design and behavior of bolted joints
    Can effectively prevent total loss of the nut – but are not very effective in preventing substantial loss of preload


The U.S. Navy's Naval Ships' Technical Manual; S9086-CJ-STM-010/CH-075R2
    The primary purpose of safety wiring is to prevent complete loss of a fastener. It's not particularly effective in preventing minor relative nut and bolt rotation and subsequent loss of preload.
It's effective in preventing complete loss of the fastener. It is, however, an ineffective
method for preventing loss of preload; some rotation can still occur, even with the best of tying techniques.

Safety wire may be used to replace previous existing safety wire. If loose or broken wires or
loose fasteners are found at disassembly, however, self-locking fasteners may be installed at reassembly


Verein Deutscher Ingenieure, Systematic Calculation of High Duty Bolted Joints.  Joints with One Cylindrical Bolt  VDI 2230, Part 1
Listed  3rd of 4 "Positive locking" methods in table A14.


    Safety cable or wire is not a means of obtaining or maintaining torque, but a safety device used to prevent disengagement of the part.


NASM1515 Fastener Systems for Aerospace Applications
(Formerly MIL-STD-1515)
    Self-locking fasteners are preferred over auxiliary devices (such as cotter pins, safety wire, tab washers, etc.)

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