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 in some applications.

[1] Both M-LOK and KeyMod enable the user to have a slimmer, lighter, smoother and more fenestrated handguard/fore-end with accessories and gadgets mounted only where needed as compared to a Picatinny handguard, which typically has whole length rail slots, resulting in a heavier weight, bulkier handguard and poorer barrel ventilation, resulting in the barrel overheating more quickly.

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 M-LOK rail specification included metric dimensions instead of imperial, and utilizes a T-slot nut capable of only 90-degree rotation, reinforced by thread-locking fluid, making it suited for applications on free-floating handguards.

In 2016, Colt Canada developed and released the Modular Rail Rifle (MRR) that uses a monolithic upper receiver with the M-LOK attachment system.

[2] In 2017, several companies produce M-LOK handguards as well as accessories like Picatinny rail strips, vertical foregrips, bipods, sling adaptors, and flashlight mounts.

NATO standards conform military issued assault rifles like the CAR 816 have semi-automatic only export versions featuring M-LOK rails on the handguard to better meet civilian market preferences in the United States.

[10][11][12] The quarter-turn T-slot nuts have different torque specifications depending on the handguard material: 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).