M-LOK

M-LOK, for Modular Lock, is a firearm rail interface system developed and patented by Magpul Industries. 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 in some applications. 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 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.