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M-LOK vs Picatinny: A Guide to Mounting & Rail Systems

M-LOK, Picatinny and KeyMod explained — how each rail interface works, what's compatible, and how to mount lights, slings and bipods.

  • By Onyx Armaments
  • 1 min read
Magpul M-LOK QD sling mount beside a Magpul RSA rail sling attachment, illustrating our M-LOK versus Picatinny mounting guide

Mounting a light, sling, bipod or grip starts with understanding your rifle's rail interface. The two systems you'll meet most are M-LOK and Picatinny — here's how they differ and how to mount accessories with confidence.

Picatinny (1913): the universal standard

The Picatinny rail (MIL-STD-1913) is a continuous row of raised slots that accessories clamp directly onto. It's the long-standing universal mount — almost any optic, sight, grip or light with a Picatinny clamp will fit. The trade-off is weight and bulk: a full rail is heavier, and the sharp edges can be uncomfortable without rail covers.

M-LOK: the modern, slimmer system

Developed by Magpul, M-LOK uses a series of slots cut directly into a lightweight handguard. Accessories (or M-LOK adapters) bolt on with a T-nut that locks into the slot — secure, repeatable and far slimmer than a quad rail. It's now the dominant standard on modern handguards. Mount lights, sling points and bipods directly to M-LOK, or add a short M-LOK Picatinny rail section for optics that need it. Browse everything in our M-LOK Accessories collection.

What about KeyMod?

You may still see KeyMod, an earlier slotted system. It largely lost out to M-LOK and is now uncommon — if you're building fresh, M-LOK is the safer long-term choice.

Schematic top view comparing a Picatinny rail with cross-slots, M-LOK rectangular slots and KeyMod keyhole slots
Picatinny, M-LOK and KeyMod seen from above. Schematic, not to scale.

Mounting the essentials

Our recommendations

For most modern builds, M-LOK keeps things light and clean. Browse M-LOK Accessories, Bipods & Mounts and Slings & Sling Mounts to kit out your rail — £5 tracked UK delivery on everything.

Related guides: AR-15 Grips Explained · Choosing an AR-15 Stock · Ambidextrous Controls Guide

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