What Does Mil-Spec Mean? Definition & More
Our quarry today falls somewhere outside, solely aviation-related. Instead, we will deep-dive into the world of Mil-Spec and Mil-Standard. Mil-Spec and Mil-Standard are short for “military specification” and “military standard.” In a nutshell, there are certain standards that just about everything in the military must meet, at least on the tactical front. Does this mean that Mil-Spec or Mil-Standard means the product or material exceeds civilian standards? Not even close. It only means that there are sets of standards set forth to the military branches and the Department of Defense (DoD) that must be met if it is required of the item. So let’s take a look at these and see what they mean and how they impact the acquisition and procurement process.
What is Mil-Standard?
There are a few differences between MIL-SPEC and MIL-STD, so let's take a look at what they are.
The military is a world of symmetry. From your first day in basic training or boot camp, you realize it is a world of right angles and complete uniformity. You are designed from the ground up to be a round peg for a round hole.
What does this mean?
There are few one-off items in the military, from people to machinery. Everything is made to transfer easily from one unit to another, from one offensive front to another, and so on. If you are a helicopter mechanic at Fort Riley, you will transfer to Fort Drum and still work on the same helicopters with very little transition. Just as there is a sort of unwritten MIL-SPEC for personnel (all military members are trained in the same things to be interchangeable within their specific branch and skill), all equipment used in the military must meet certain specifications. The whole reason for this is to ensure interoperability throughout the entire scope of operations. For instance, a uniform purchased at Joint Base Dix is the same as one bought at Fort Bliss. All uniforms must be MIL-SPEC. Uniforms are the simplest item that this applies to; MIL-SPEC is applied to tens of thousands of items. MIL-SPEC are just specifications that these items must meet. I.e., tensile strength on hardware, thread count on uniform tops and trousers, etc. MIL-STD is instead a document that establishes a uniform set of engineering or technical requirements. These are for military-unique procedures, practices, methods, etc.
There are five types of MIL standards:
- Interface standards
- Design criteria standard
- Manufacturing process standards
- Standard practices
- Test method standards
MIL Standards came out of World War II. The U.S. worked in tandem with dozens of countries, and all of those countries used their own equipment, small arms, artillery, etc. For instance, the British used the .303 Enfield, which was a wonderful caliber. However, it was so similar in size and capability to the American .30-’06 Springfield, but not interoperable. Any surpluses in their ammunition couldn’t be used in our weapons, and vice versa. Also, as the war struck on, American equipment entered our allies' fleets. The problem with this was that our hardware, drivetrains, tires, and everything did not match theirs. The result was increased interoperability of equipment. For instance, we saw the introduction of standardized ammunition calibers (9x19mm, 5.56x45mm NATO and 7.62x51mm NATO), but also standardized hardware, hardpoints for munitions, standard cannon calibers on aircraft, and much more.
It also ensures that hardware across the U.S. platform will be congruent. You can be assured that an AN-fittings that work on the F-16 program will work on the B-1. Tridair fasteners from the B-1 work on F-15s, and so on.
At least in theory, this will save enormous amounts of money and effort. However, in practice, it has had a habit of stovepiping ingenuity.
What Does Mil-Spec Apply to?
So, if MIL-STD applies to the standards, what is MIL-SPEC?
Military standards are overarching engineering specifications; standards are the specifics that each item must meet for procurement. And this is hundreds of thousands of items. Maybe even millions. There are also thousands or tens of thousands of pages of MIL-SPECs. They cover literally every aspect of every piece of tactical machinery.
Now, it is important to differentiate something here: not everything bought and procured by the DoD must be MIL-SPEC. The military buys thousands of pieces of construction equipment every year like
- Road graders
- Agriculture tractors (mainly for airfield mowing operations)
- Utility tractors
They also own and lease many thousands of light, medium, and heavy trucks for public works, utility work, and much more.
These are not tactical vehicles; these are garrison support vehicles. Vehicles that stay in the garrison and are not used in the field do not have to adhere to MIL-SPEC criteria. MIL-SPEC is specifically made for tactical vehicles and equipment that are used in tactical environments. The interesting thing about MIL-SPEC is that the U.S. government often owns the rights to the component, allowing other vendors to compete in the marketplace for the item. If Rockwell made the part, but the U.S. government owns it, then any vendor meeting MIL-SPEC standards can replicate and sell it. Saying an item is “MIL-SPEC” or “mil spec” is an informal way to express that the item, whatever it may be, meets a specific standard or specification. Of course, they have to back that up by providing proof that it is MIL-SPEC compliant. Why
How are Mil-Specs and Aerospace Specifications Related?
There is a significant crossover in the aerospace world between MIL-SPEC and meet aviation standards. This is no surprise when considering it from a historical perspective: most of the major advances in aerospace and aviation occurred during World War II and shortly thereafter. The jet age was ushered in at the end of World War II, and the Rocket Age was also. It should come as no surprise that the same military aircraft manufacturers would also build commercial aircraft.
Taking Boeing for example. Boeing produced the KC-135 from 1955 through 1964, which still fly daily. The KC-135 is not a B707, but it shares a lot of similarities. While no longer flown commercially, they are both still used in the Air Force. But it takes only a casual glance to see the lineage of these two in the current fleet. It makes sense to use MIL-SPEC items interchangeably between the civilian production line and military aircraft for cost control and simplicity of design. Also, they know that their aircraft will be marketed for defense use. Take the P-8 Poseidon and the KC-46 Pegasus. These are both variations of the B737 and B767, respectively. Knowing that their aircraft will probably be pitched for military service, they use MIL-SPEC materials as much as possible to keep from reengineering. But again, so many modern aircraft are both used for defense and civilian roles and derived from military technology that it makes no sense to design them outside of MIL-SPEC.
Also, though, so many of the airframe components, like hydraulics, hardware, electric connectors, wiring, and so on, are MIL-SPEC to begin with, so there is no reason to deviate. For instance, AN-fittings, which are used in all commercial aircraft, military aircraft, and about a thousand different applications outside of aviation, are MIL-SPEC. There are no better fittings for hydraulic systems, so they are used in commercial and military aircraft.
Why Use Mil-Spec Components?
Diving a little deeper into the intersection of MIL-SPEC parts usage and commercial or military applications, and we have already answered what MIL-Spec is, let’s explore why you would use MIL-SPEC components. For defense operations, it is the rules. There is no getting around it; if the platform requires MIL-SPEC components, they must be used. In the civilian world, there is a sort of expectation that MIL-SPEC will lead to a better component grade. We see it in marketing all the time.
“Military grade hardware.”
“Aviation grade, mil-spec aluminum.”
And so on.
But that doesn’t necessarily mean much of anything unless you are procuring parts or components for a military vehicle.
To be certified as MIL-SPEC is not to be any better than anything else; if anything, it may be outdated because the approval process is so long. All it means is that the component meets MIL-SPEC standards.
Understanding Where to Get Quality Mil-Spec Components
MIL-SPEC components and parts are not necessarily branded individually as such. Think about a screw or a bolt. Millions of them might be in circulation, used across a dozen different airframes. Instead, the part number or stock number bears the branding of a MIL-SPEC item. For instance, an MS35202 is a common screw used across multiple branches and aircraft.
Longevity of Mil-Spec Parts
Part of the MIL-SPEC could be a definition of the expected lifespan. This metric is hard to gauge accurately, but limits can be placed on how long the item will last. But the thing is, there are so many variables involved. Is the aircraft used exclusively stateside, or is it operating in theater? Is it a tactical aircraft that flies close air support or strike missions, or does it orbit for twelve hours at FL410? Both aircraft types use MIL-SPEC parts, but the one flying straight and level and pulling 1-G will be much less hard on components. This is why having a stockpile of parts is so important because there is no telling what the actual longevity will be. The specifications can say one thing, but it doesn’t mean that there won’t be an event that causes the part to fail prematurely or to exceed the expectation.
Is Mil-Spec Better?
Bearing a MIL-SPEC branding does not make the part better. In fact, it might not even make it any different than an identical commercial off-the-shelf part or component. It only means that the part meets MIL-SPECs that were assigned to the part or component. It is the DoD's way of ensuring that all parts meet a common standard.
It is so there is no confusion about whether this clamshell connector or that one, which came from different vendors, meets the standard.
Many misconceptions are floating around about the superiority of MIL-SPEC parts. There may be no difference between MIL-SPEC and a commercial part other than the part number. But if the military application demands MIL-SPEC, you must procure MIL-SPEC. Greenwood Aerospace is your MIL-SPEC procurement service. We specialize in procurement, storage, and MIL-SPEC packaging. If you are in this space and need to establish a supply of MIL-SPEC parts, give us a call or start a quote today!