science

Safety wire

Safety wire is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Safety wire rather than just read about it. In short: A safety wire or locking-wire is a type of positive locking device that prevents fasteners from falling out due to vibration and other forces. The presence of safety wiring may also serve to indicate that the fasteners have been properly tightened.

Key takeaways

Safety wire belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Safety wire to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Safety wire from memory before moving on to harder problems.

Reference excerpt

A safety wire or locking-wire is a type of positive locking device that prevents fasteners from falling out due to vibration and other forces. The presence of safety wiring may also serve to indicate that the fasteners have been properly tightened. Safety wire is available in a variety of gauges and materials, depending on the application. In aircraft and racing applications, stainless steel wire is used, such as in 0.8 mm (0.032 in) diameter. Typically, the wire is threaded through a hole drilled into a fastener or part, then twisted and anchored to a second fastener or part, then twisted again.

Application

Principle There are a few techniques for different applications. The word safetying is universally used in the aircraft industry. Briefly, safetying is defined as: "Securing by various means any nut, bolt, turnbuckle etc., on the aircraft so that vibration will not cause it to loosen during operation." These practices are 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. The wire itself maintains tension and remains in place by being twisted around itself and attached to the fastener to be secured on one end and an anchor point (which could be another fastener) on the other end. Since safety wire is made of a malleable alloy, it retains its shape after being bent, rather than springing back to its original shape. This property allows it to remain locked around an object, such as when it is passed through a small hole on a fastener, looped back upon itself and then twisted. The same process is then repeated around the anchor point, which could be another fastener. Since it remains twisted instead of unraveling, it acts as a fixed loop and will not back out without considerable force (greater than the stresses which it is intended to counter) being applied.

Mousing (pronounced ) is the application of a molly or safety wire, called mousing wire in this use, to secure a threaded clevis pin to a shackle. This is done by passing a couple of turns of mousing wire through the reach-hole provided for this purpose in the unthreaded end of the clevis pin and around the body of the shackle's hoop. Alternatively, some threaded shackles are provided with a hole through the threaded end of the pin beyond where it emerges from the threaded hole. A cotter pin or a couple of loops of mousing wire through this hole serves the same purpose and secures the shackle in a closed position. Nylon zip-ties are also commonly used in applications where the shackle must be secured but easy removal is required.

Use A safety wire is used to ensure proper security for a fastener. The wire needed is long enough to reach from a fixed location to a hole in the removable fastener, such as a pin — a clevis fastener, sometimes a linchpin or hitch-pin through a clevis yoke for instance — and the wire pulled back upon itself, parallel to its other end, then twisted, a single end inserted through a fastener, and twisted again, possibly then anchored to a second fastener or other part, then twisted once again, having excess slack pulled relatively taut to be secure. The two ends of the wire-loop thus formed are joined by twisting them together with a tool, using enough twists to be secure, then released from the twisting tool. The removable fastener — possibly a nut, wing nut, turnbuckle, a bolt or a pin similar to a bolt — having a hole through a part of it that will remain accessible when it is fastened in place will be secured with the wire passing through it. When finished, any excess length of wire would be cut off with a pair of wire cutters, such as pliers that may, also, be the twisting tool. If the fastener part to be secured does not come with a hole for the safety wire, one may need to be drilled. Safety wire is not reusable, thus it can be cut apart in order to remove it easily when the fastener is to be opened.

Proper techniques When using a most common gauge of safety wire, which is 0.8 mm (0.032 in), guidance for installation can be found in several publicly available sources. FAA AC 43.13-1B, MS33540, and FAA AC 43.13-1B identifies only 6 to 8 twists per inch (about 6 to 4 mm pitch). 43.13-1B has no other reference to twists per inch either by hand twisting with special tools. Aviation Mechanic Handbook identifies different twists per inch as 0.020–0.025 in (0.5–0.6 mm) at 8–14 twists per inch (~3-2 mm pitch), 0.032–0.041 in (0.8–1 mm) at 6–11 twists per inch (~4 to 2 mm pitch), and 0.051–0.060 in (1–2 mm) at 4–8 twists per inch (~6-3 mm pitch). The safety wire should be threaded through the object fastener such that it creates tension in the opposite direction of the fastener's removal. For example, if a standard automotive bolt in the U.S. is being secured, then the safety wire when installed should put tension on the bolt in a clockwise direction, since that is the direction that the bolt turns to tighten. When drilling a fastener, the choice of where to drill it depends on the type of fastener and to what it will be wired. The alternative to drilling holes in fasteners is to use safety wire tabs (see Safety wire tabs section below), or to purchase pre-drilled fasteners. AC43.13-1B, par. 7-124 f. page 7-21 specifies "Safety wire ends must be bent under and inward toward the part to avoid sharp or projecting ends, which might present a safety hazard." The first picture in this article does not conform to proper techniques and practices and ought to be replaced with a better example.

… excerpt ends here. Continue reading the full article.

Illustrations

Safety wire: A moused shackle — A moused shackle

Safety wire: A "pignose" safety wire twister — A "pignose" safety wire twister

Safety wire: Safety wire pliers — Safety wire pliers

Worked examples

Example 1 — a first encounter with Safety wire

Start with the simplest possible case. Write down what Safety wire claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Safety wire before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Safety wire ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Safety wire

In research: Safety wire appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Safety wire in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Safety wire is common in secondary-school and first-year university syllabi. It links to neighbouring topics Fasteners, Safety equipment, so understanding it makes those chapters shorter.
In everyday life: Look for Safety wire outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Safety wire in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Safety wire means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Safety wire out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Safety wire in simple terms?

Why does Safety wire matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Safety wire?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Safety wire.