M-LOK vs Keymod - What’s the Difference? thumbnail image

M-LOK vs Keymod - What’s the Difference?

80 Percent Arms   |   Feb 5th 2020

The incredible modularity and individuality of the AR platform is largely due to the ability to stick almost anything on the handrail. From lights, lasers, grips, bipods, or even bayonets, the handrail can fit more accessories than you would ever need. While both M-LOK and Keymod mounting systems can accommodate the same accessories that does not mean these systems are created equal. Read on to understand the differences between the two, and which style might fit you best.


keymod rail

Bravo Company USA was one of the last KeyMod holdouts before the industry adoption of MLOK

Resembling an antique key-hole, it’s easy to see how the Keymod rail design got its name. This style of mount makes the physical act of attaching your accessories extremely easy. Simply take the lug or “male end” of your Keymod attachment and insert it into the larger round end of the handrail or “female end”, now slide the attachment forward in the Keymod hole, and tighten the lug to secure the attachment. This style has been around for a long time (well, longer than MLOK) and you will have absolutely no issue finding your desired accessories in this mounting style.


  • Many high quality manufacturers produce this style, so quality parts are easily obtainable
  • Once tightened, the Keymod style will self-align your accessories for you
  • No special tools required to tighten or modify your system in the field


  • There is some concern about security of your accessories if the rifle is dropped or bumped the wrong way
  • Many low quality manufacturers also produce this style, and fitment may vary from brand to brand

M-Lock or (Modular Lock)

mlok rail

MLOK rails can always be identified by the "M" logo on them, and the straight attachment notches

In contrast with Keymod, the M-LOK system is simply a rectangular slot that you will insert your attachments into, and with the help of a T-shaped nut that will turn perpendicular to the hole --lock it in place. Originally designed by Magpul, this design is only available from manufacturers that Magpul has approved. While some people disagree with this, I lean towards appreciating this decision; as it only lets reputable and quality manufactures produce this style—keeping fitment and quality uniform.


  • Only certain brands are allowed to produce this style, helping to keep all MLOK rails high quality with uniform fitment
  • Locking mechanism is much more secure than Keymod
  • Many prefer the aesthetics of M-LOK to Keymod
  • Ability to mount your accessories to any part of the MLOK design, whereas Keymod makes you insert into one set position


  • M-LOK does not self-align like Keymod does, so more care is required when attaching your tactical bayonet
  • Offers less brand choices for the customer

Opinions of SOCOM


US SOCOM recently adopted the Geissele URG-I MLOK upper

After rigorous head to head testing for the US SOCOM contract, it was  reported by Crane Division that Keymod had major issues with retaining attachments on the rifle after being dropped from various heights. MLOK was recorded as having a perfect record in this subject, which may put some doubt in the minds of the consumer when buying a Keymod style rail. Now let me be clear: 99.99% of us are not going to be pushing our equipment to even a fraction of the limit that our troops do. So is this information really relevant to the average consumer choosing MLOK vs Keymod?—probably not. However there are those of us (myself included) who want the best of the best equipment possible, for no other reason than we just want it.

So Which Should I Choose?

Much like caliber, brand, configuration, or anything else in this industry: you choice of rail style really boils down to personal preference. I myself use solely M-LOK, because if its good enough for our troops, its dang sure good enough for me. Keymod is a valid option, but it just doesn’t do anything really that MLOK doesn’t, and also doesn’t do anything better, plus it looks a little like.... well, you know. Test both styles and find out for yourself what you prefer, because if everyone just blindly took my advice…well society would be in utter shambles.

Check out 80% Arms large selection of high quality MLOK and Keymod  upper recievers!! If you already have an upper, we also carry a large selection of MLOK accessories! Available in different styles and colors, 80% Arms has you covered!