Magpul MOE M-LOK handguard on a privatly assembled AR-15

M-LOK, for Modular Lock, is a firearm rail interface system developed and patented by

Magpul Industries Magpul Industries Corporation is an American designer and manufacturer of high-tech polymer and composite firearms accessories like M-LOK. Magpul Industries takes its name from its first product, the MagPul (Magazine Puller), an accessory for th ...

. The license is free-of-charge, but subject to an approval process. M-LOK allows for direct accessory attachment onto the "negative space" (hollow slot) mounting points, and is a competing standard to VLTOR's open sourced KeyMod system for replacing the ubiquitous

Picatinny rail The Picatinny rail ( or ), or Pic rail for short, also known as a MIL-STD-1913 rail, 1913 rail or STANAG 2324 rail (cancelled), is a military standard rail interface system that provides a mounting platform for firearm accessories. It was ...

in some applications. Compared to the Picatinny rail system, both M-LOK and KeyMod enable the user to have a slimmer, lighter, smoother and more fenestrated

handguard A barrel shroud is an external covering that envelops (either partially or full-length) the barrel of a firearm, to prevent unwanted direct contact with the barrel (e.g. accidental collision with surrounding objects, or the user accidentally tou ...

/ fore-end with accessories mounted only where needed, whereas a Picatinny handguard typically will have rail slots for its whole length, resulting in a heavier and bulkier handguard with sharp edges and poorer barrel ventilation. The M-LOK system can be seen as an evolution of the Magpul Original Equipment (MOE) system, but the two are not fully compatible. Though newer M-LOK accessories can be used on older MOE slot handguards if an adaptor plate is used, there is no adaptor available for using older MOE accessories on the newer M-LOK handguards.

History

A prototype of the MOE slot was revealed by Magpul in late 2007 together with their Masada Concept Rifle (which would later be known as the

Adaptive Combat Rifle The Adaptive Combat Rifle (ACR) is a modular assault rifle designed by Magpul Industries of Austin, Texas, and known initially as the Masada. In late January 2008, Bushmaster Firearms International entered into a licensing agreement with Magpul ...

). The MOE slot system was released by Magpul in 2008 as a feature on their MOE handguards, and at the same time compatible accessories such as Picatinny rail sections, direct MOE mounted light mounts, grips, bipod studs, etc. were released. The MOE slot standard was never officially released, and a drawback to the system was that the rear side of the panel had to be accessed in order to mount accessories, limiting its application. The MOE slot system uses a weld nut which has to be placed manually on the inside of the handguard before mounting, making the slot system unsuited for applications such as free-floating handguards. Also, depending on the accessory item, the spacing increments between the MOE slots were not small or uniform enough to adjust the desired placement of accessories. Acknowledging shortcomings of the MOE systems, Magpul drafted M-LOK as a new and improved mounting standard which was released in 2014 replacing the existing MOE slot. The M-LOK rail specification included

metric Metric or metrical may refer to: * Metric system, an internationally adopted decimal system of measurement * An adjective indicating relation to measurement in general, or a noun describing a specific type of measurement Mathematics In mathem ...

dimensions instead of imperial, and utilizes a

T-slot nut A T-slot nut is used with a threaded clamp to position and secure pieces being worked on in a workshop. The T-slot nut slides along a T-slot track, which is set in workbench or table for a router, drill press, or bandsaw. T-slot nuts are also use ...

capable of only 90-degree rotation, reinforced by

thread-locking fluid Thread-locking fluid or threadlocker is a single-component adhesive, applied to the threads of fasteners such as screws and bolts to prevent loosening, leakage, and corrosion. Most thread-locking formulas are methacrylate-based and rely on t ...

, making it suited for applications on free-floating handguards. It was designed to work with both metal and polymer parts. M110A1_SDMR

In 2016,

Colt Canada Colt Canada (formerly called Diemaco) is the Canadian division of American firearms manufacturer Colt located in Kitchener, Ontario, Canada. The facility produces small arms for the Canadian Armed Forces, Canadian law enforcement agencies In ...

developed and released the Modular Rail Rifle (MRR) that uses a monolithic

upper receiver In firearms terminology, the firearm frame or receiver is the part of a firearm which integrates other components by providing housing for internal action components such as the hammer, bolt or breechblock, firing pin and extractor, and has th ...

with the M-LOK attachment system. In 2017, several companies produce M-LOK handguards as well as accessories like Picatinny rail strips,

vertical foregrip A vertical forward grip or foregrip is a vertical pistol grip mounted on the fore-end of a long-barrel firearm, designed for grasping by the frontal support hand (or "off hand"). Use Forward grips aid in the maneuverability of the firearm, ...

bipod A bipod is a V-shaped portable attachment that helps support and steady a device, usually a weapon such as a long gun or a mortar. The term comes from the Latin prefix ''bi-'' and Greek root ''pod'', meaning "two" and "foot" respectively. Bip ...

s, sling adaptors, and flashlight mounts. In 2017, a summary report of testing conducted by NSWC-Crane for

USSOCOM The United States Special Operations Command (USSOCOM or SOCOM) is the unified combatant command charged with overseeing the various special operations component commands of the Army, Marine Corps, Navy, and Air Force of the United States Ar ...

indicated that, while comparable in endurance and rough handling testing, M-LOK greatly outperformed Keymod in repeatability, drop testing and failure load testing.

Licensing

While M-LOK is licensed free-of-charge, it is not open source, and thus manufacturers must acquire a license from Magpul before making products using the M-LOK standard. Magpul claims this gives them more control in assuring that all M-LOK products are made to specifications ensuring compatibility. Program participation is open to any interested manufacturer. Note that although Magpul describes the license as a "free license", the meaning does not match the more common meaning originally established in computer circles. The computer "free license" refers to a freedom to use,Open Definition 2.1
on opendefinition.org ''"This essential meaning matches that of “open” with respect to software as in the Open Source Definition and is synonymous with “free” or “libre” as in the Free Software Definition and Definition of Free Cultural Works."'' while Magpul only conditionally offers the license for free (analogous to a

source-available Source-available software is software released through a source code distribution model that includes arrangements where the source can be viewed, and in some cases modified, but without necessarily meeting the criteria to be called open-source ...

freeware Freeware is software, most often proprietary, that is distributed at no monetary cost to the end user. There is no agreed-upon set of rights, license, or EULA that defines ''freeware'' unambiguously; every publisher defines its own rules for t ...

Technical specifications

Rail specifications

The slot dimensions (used on handguards, etc.) are available on the web. The slots provide

length intervals, and accessories can be mounted either within a slot or bridging between slots, making it possible to adjust the position of accessories in smaller intervals than the length of the slot. The slots on an M-Lok handguard are approximately long and wide and space from each other. The radius of the corners is approximately .

Attachment specifications

The quarter-turn

s have different

torque In physics and mechanics, torque is the rotational equivalent of linear force. It is also referred to as the moment of force (also abbreviated to moment). It represents the capability of a force to produce change in the rotational motion of th ...

specifications depending on the handguard material: * for attaching metal accessories to metal handguards. * for attaching polymer or metal accessories to polymer handguards. * for attaching polymer accessories to metal handguards. Attachment screws made by many U.S. manufacturers are often either #8-32 TPI or 10-24 TPI UNC threads, which respectively have major thread diameters of 0.1640 inches and 0.1900 inches (4.166-0.794 mm and 4.826-1.058 mm expressed in metric designation). Many M-LOK screws on the international market instead use either M4 or M5 metric threads to reduce cost. The tool required for mounting, in addition to the thread size, also depends the screw head type. Hex keys are used extensively in the firearms industry, but metric and imperial hex keys as a general rule are not compatible. It is possible to damage the tool and screw by selecting a tool that is too small for the fastener, which can be done by using an imperial tool on a metric fastener, or the converse. An exception to this is 4 mm hex keys, which are almost the exact same size as . In many industries, this makes hex keys preferred for consumer products because end users can successfully use an imperial key on a metric fastener, and vice versa. While screw and slot dimensions are available on the web, the T-slot nut dimensions are currently under review by the

US State Department The United States Department of State (DOS), or State Department, is an executive department of the U.S. federal government responsible for the country's foreign policy and relations. Equivalent to the ministry of foreign affairs of other nati ...

to determine whether it should be regulated by

ITAR International Traffic in Arms Regulations (ITAR) is a United States regulatory regime to restrict and control the export of defense and military related technologies to safeguard U.S. national security and further U.S. foreign policy objectiv ...

, and until it is clarified drawings are only available to

US citizens Citizenship of the United States is a legal status that entails Americans with specific rights, duties, protections, and benefits in the United States. It serves as a foundation of fundamental rights derived from and protected by the Constitu ...

. File:M-LOK 1.png, M-LOK handguard and attachment parts File:M-LOK dimensions.jpg, M-LOK approximate slot dimensions. (Primary measurements in millimeters, inches in parenthesis.)

References

"KeyMod vs. M-LOK Modular Rail System Comparison", Presented by Caleb McGee, Naval Special Warfare Center Crane Division, 4 May 2017; Abstract #19427

External links

* {{Firearm accessories mounting standards Mechanical standards Firearm components