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Understanding Mil Spec Cable: An In-Depth Guide to MIL-DTL-83420

Monday, April 29, 2024

Mil-Spec, or Military Specification, is the term used to describe a set of governing standards for manufactured components that honor a rigid set of quality and manufacturing requirements defined by the United States Department of Defense (DoD).

Broadly speaking, Mil-Spec materials are those that have satisfied a battery of standards that address matters like materials selection, manufacturing design, quality testing, and of course manufacturing and validation processes themselves.

The function of Mil-Spec standards is to ensure that products used in US military applications (and aircraft) meet a standard of uniformity, specifically even when multiple makers are producing the same part. Equally important to uniformity, Mil-Spec-approved parts certify that performance will be at optimal, anticipated levels, and again, across any maker’s parts that are meant for use within military applications.

Alongside uniformity and performance is durability. Because military equipment is routinely deployed in harsh, threatening, or in some other ways, unconventional environments, durability must also reach a strata of reliability worthy of the most challenging military and natural environments, including, of course, those found amid battle conditions.

Lastly, Mil-Spec promises that parts are safe for use, across a wide assortment of hazardous conditions. Specifically due to the military’s need to protect the lives of its personnel, partners, allies, and interests, Mil-Spec standards must include requirements that assure everyone a safe operational experience. Any malfunction of operations-critical Mil-Spec components could mean a loss of human life, lives, and infrastructure.

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MIL-DTL-83420 Standards

While Mil-Spec products of a wide array are produced in the United States, in the specific production of cable/wire rope for aircraft control applications, the Mil-Spec manufacturing rubric applied is known as MIL-DTL-83420. Essentially a “rule book,” MIL-DTL-83420 dictates the precise requirements manufacturers must fulfill to assign the Mil-Spec designation to cables used for aircraft control systems.

As one would expect, the MIL-DTL-83420 document is a detail-rich, itemized telling of requirements such cables must satisfy.

For instance, MIL-DTL-83420 begins with the scope of the cable material itself. Strict standards for the temperatures the cable can tolerate are stipulated in this portion of the document. Under scope, for example, temperature requirements are set at -65 °F and +250 °F (-54 °C - +121 °C). These incredibly polarized temperature ratings must be met due to an aircraft’s exposure to wind, fuel, oils, dust, and other potentially harmful conditions and particulates.

In addition to standards set for temperature tolerances, the cable must adhere to a classification standard that dictates the types and compositions of wire rope. Slightly further down the document, the scope includes the types of cable, Type I: nonjacketed, or Type II: jacketed, for example. Beyond the classification of the cable is composition, which addresses the cable material’s chemical composition, such as, but not limited to, carbon steel, corrosion-resistant steel, such as 304 stainless steel, or zinc-coated steel, otherwise known as galvanized wire rope, and so on.

Cable assembly utilizing mil-spec cable & ball fittingCable assembly utilizing mil-spec cable & ball fitting
Cable Assembly Utilizing Mil-Spec Cable & Ball Fitting

A cable that does not demonstrate its ability to function predictably within these strict regulatory margins is simply unworthy of being used in control components found in aircraft – no matter the craft’s military, recreational, or commercial uses.

From scope, the document unpacks applicable documents that, when required, operate as regulatory cohorts to MIL-DTL-83420. In applicable documents, the word, “applicable” is operative, inasmuch as additional defense specifications are identified, where a Mil-Spec cable’s elements extend beyond being only a length of wire rope itself. Take, for instance, coated cable for a Mil-Spec application. Well, in this case, MIL-DTL-83420 has precise coating material requirements, that, like standards set for exposure to extreme climates, must also meet inflexible criteria.

Another example of the need for additional applicable documents would be in cases where multiple components comprise a completed product. A Mil-Spec cable, for instance, that includes a ball fitting swaged to each end of a fixed length of cable is known as a cable assembly. In this particular example, the Mil-Spec cable includes wires stranded into cable, two end fittings, and perhaps less obvious, a swaging operation used to join the fittings to the wire rope. In this use case, a cable was produced, which was made, we’ll say, from 304 stainless steel. The wire, its chemical composition, and its design are all variables that must honor the terms set in MIL-DTL-83420. Furthermore, the swaging operation used to apply fittings to a cable is also subjected to the scrutiny of MIL-DTL-83420 through a series of quality and validation exercises that follow manufacturing.

Because the cable contains additional components, additional applicable documents must be identified alongside MIL-DTL-83420. Essentially, MIL-DTL-84320 instructs manufacturers on virtually all facets of the materials used to produce Mil-Spec parts, as well as the regulatory requirements surrounding production operations.

Mil-Spec cable requirements are the next topic addressed in MIL-DTL-83420 and herein resides the lifeblood of the document.

Within the requirements, section of this governing military standard are matters such as cable material type – stainless steel, galvanized steel, coating materials, and so on, as well as cable construction, which is the term used to categorize the geometric orientation with which a cable’s wires are helically bound together to form a wire rope.

Lastly, manufacturing operations, quality testing, finishing (if lubricants are required), as well as verification, packaging, marking, and final inspections all round out the parameters addressed in MIL-DTL-83420.

While this article seeks to provide a detailed account of the nature and characteristics of MIL-DTL-83420, it is not meant to be comprehensive and should not be treated interchangeably with documentation provided directly from the Department of Defense and/or other authoritative bodies.

What is Military (Mil-Spec) Cable?

Mil-Spec cable is mechanical wire rope that meets or exceeds manufacturing standards defined by the US Department of Defense, as outlined in a document known as MIL-DTL-83420.

However, Mil-Spec cable, taken as cable alone, does not depart from wire ropes used in virtually limitless industrial, MedTech, automotive, and commercial applications. As a matter of fact, and by way of example, 304 stainless steel cables found suspending patio lighting, or actuating the end effectors of an endoscope, could easily be identical to the cable producing motion in the vertical stabilizer of a military or commercial aircraft.

So, then what exactly makes mechanical cable or a cable assembly a Mil-Spec cable or assembly?

The answer is the meeting of rules defined in MIL-DTL-83420.

A stainless steel cable meant to support patio lighting answers to different standards because what the cable is being asked to do is not remotely identical to that which a Mil-Spec cable will be asked to shoulder.

As mentioned above, Mil-Spec cable is used in both military and aircraft control applications. Therefore, cables produced by a Mil-Spec cable maker must possess the supply chain, engineering, quality, and manufacturing capacity capable of meeting or exceeding rules set in Mil-Spec regulatory documents, like those discussed in MIL-DTL-83420. Accordingly, outside of the materials, manufacturing, testing, validation, packaging, and marking standards defined by the US Department of Defense, the cable is basically the same as that which can be used to effortlessly suspect one’s patio lighting, for instance.

S064 - Stainless Steel Cable, Bare 7x7, Mil Spec

What precisely sets Mil-Spec cable apart from other identical cables are matters that deal entirely with processes.

MIL-DTL-83420, for instance, defines meticulous parameters for the number of strands used, as well as the construction configuration of a given wire rope. Wire diameter is also discussed in MIL-DTL-83420 in such a way as to ensure strict tolerances for dimensions are measured, tested, and ultimately met. Wire material suppliers' parts, as well as other sources of raw materials, are all among the wide body of variables that undergo austere evaluation through MIL-DTL-83420, once required materials are formed into functioning Mil-Spec parts. This promises that the manufacturing, testing, qualifying, and validating process all fall within the defined parameters articulated in MIL-DTL-83420.

Below, you’ll find a useful chart that outlines the more common wire rope component standards addressed in MIL-DTL-83420. Please note however that the very best and most comprehensive source of information on MIL-DTL-83420 can be found either by consulting the ASSIST Service, provided by the Department of Defense website or by downloading MIL-DTL-83420 through Carl Stahl Sava Industries’ website.

MIL-DTL-83420 | Reference Guide

Topic MIL-DTL-83420 Section Where It’s Discussed
Wire Rope Materials and Classification Section 3.3, and 1.2 respectively
Ductility of Steel Section
Coating Material and Composition Section 3.3
Lubricant Material Section 3.3.4
Minimum Breaking Strength Section 3.5.3 (Mechanical Properties)
Minimum Elongation Section 3.3 (Mechanical Properties)
Corrosion Resistance Section 3.4 (Environmental)
Temperature Range Section 1.1, 3.4, 3.5.1, 3.5.9, 4.x
Abrasion Resistance 6.1

Ask a Mil-Spec Cable Expert

In summary, note that MIL-DTL-83420 focuses on technical specifications of the cable/wire rope itself, or if an assembly, the entire finished product, not the manufacturer or supplier.

To ensure that your Mil-Spec cable requirements satisfy the strict regulatory requirements outlined in MIL-DTL-83420, talk to Sava's cable experts. Sava’s been producing Mil-Spec components for more than 50 years now and deeply understands the technical requirements of both the job the cable needs to do, as well as the sophisticated bevy of requirements the US military and aircraft manufacturers must achieve to keep machines moving, aircraft soaring and operators safe from harm.

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April 29, 2024