T-slot structural framing is a framing system consisting of lengths of square or rectangular extruded aluminum, typically 6105-T5 aluminium alloy, with a T-slot down the centerline of one or more sides. It is also known as 80/20 framing, after the company 80/20, Inc., one of the prominent T-slot framing brands, the name of which is based on the 80/20 principle. While there is no published standard defining this framing system, manufacturers have settled into two categories of product comprising several series each that is generally intercompatible across manufacturers.

Profiles[edit]

T-slot framing is divided into metric and fractional (imperial) categories. The T-slot is always centered along the long-axis of the piece. Pieces are available in each series with a square cross-section. Rectangular cross sections are available as well which measure x by 2x (where x is the defined width) - e.g. 40mx80mm for 40 series.

• Slotted Holes Slotted holes can be dimensioned in several different ways. Center points on the longitudinal axis are located and the radii are indicated with a note. Linear measurements indicate the overall size of the slot and the radii are specified. A note indicates the two linear dimensions of the slot and another note specifies.
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These t slot nuts let you attach plates, brackets, and other parts to standard 20mm aluminum extrusions (with a slot opening of 6mm) with standard M5-0.8 screws or bolts (not included). They can be inserted post-assembly by dropping them into the slot. Inserting a nut into the slot and twisting with a screw locks the nut in place. The M-LOK system uses a rectangular T-Nut and a rectangular slot. To mount an M-LOK accessory: Orient the T-Nuts so that they will sit in the M-LOK slots. The accessory is correctly seated in the slot if the bottom of the accessory is flush with the mounting surface. Use a hex wrench to rotate the T-Nut 90 degrees into the locked position.

• CAD model of a rotating T-nut used with aluminium T-slots/ T-track/ extrusions

• T-nut (red) installed in a T-slot

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References[edit]

For years, the Picatinny rail was the leader in attaching lights, lasers, foregrips, and other accessories, but it had drawbacks. Adding a Picatinny rail onto a rifle’s handguard or fore-end adds extra weight, and some shooters complain about the extra bulk and “cheese grate” feeling it has on the hand. And although both the Picatinny and Weaver rail systems work great for mounting scopes, their shortcomings in accessory attachments left a lane open for improvement.

These shortfalls brought the next generation of accessory mounting: KeyMod and M-LOK. The KeyMod and M-LOK are based on a slot system rather than the rail system of the Picatinny and Weaver mounts. This means a smoother surface and more mounting options. Both gained popularity since their introduction to the market in the 2010’s — but which system is better? Keep reading to learn a little about the KeyMod vs. M-LOK systems, including how to mount accessories.

V Slot Vs T Slot

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KeyMod

The KeyMod handguard was developed as a collaboration between VLTOR Weapon Systems and Noveske Rifleworks. They released the KeyMod system to the public in 2012 in hopes of standardizing universal attachment systems. It is an open-source design, meaning the design can be used freely by any company to make rails or accessories.

Instead of having a hand guard with a picatinny rail attached, the KeyMod was designed so that accessories could be mounted directly onto the rail. This also allows for picatinny rails to be mounted onto the handguard wherever needed.

How to Mount KeyMod Accessories

The KeyMod is a modular system with the mounting slots having a key-hole profile. It is composed of two parts, the KeyMod slot and the KeyMod nut.

To mount KeyMod accessories:

1. Orient the KeyMod nut the correct way. The backer nut, which is the piece that actually goes into the KeyMod slot, protrudes on one side only at the bottom. This protrusion should face in the same direction as the muzzle of the gun. Many accessories will have an arrow to remind you of the correct orientation.
2. Place the backer nut of the accessory in the larger hole of the KeyMod slot, then slide it forward into the narrow section of the slot.
3. Screw in the accessory to give tension to hold it in place.

M-LOK

The Modular Lock, or M-LOK was patented by Magpul Industries and introduced to the market in 2014. Just like the KeyMod, the M-LOK allows for direct accessory attachment. Magpul sought a design that worked better with non-metal mount surfaces. The polymer accessories Magpul offered didn’t work well with the KeyMod’s conical nut. So, they created the M-LOK system.

Unlike the KeyMod, the M-LOK is not open-sourced, but rather free licensed. This means that manufacturers can only make products using the M-LOK standard after acquiring a license from Magpul.

How to Mount M-LOK Accessories

The M-LOK is similar to the KeyMod system in that both involve locking a nut into a slot on the rail. The M-LOK system uses a rectangular T-Nut and a rectangular slot.

V Slot Aluminum

To mount an M-LOK accessory:

1. Orient the T-Nuts so that they will sit in the M-LOK slots. The accessory is correctly seated in the slot if the bottom of the accessory is flush with the mounting surface.
2. Use a hex wrench to rotate the T-Nut 90 degrees into the locked position.
3. Continue tightening the screw to the correct torque specs:
   • Metal accessories to metal handguards: 35 in/lbs
   • Polymer/metal accessories to polymer handguards: 15 in/lbs
   • Polymer accessories to metal handguards: 15 in/lbs

KeyMod vs. M-LOK – Which is Better?

In 2016, the United States Special Operations Command (USSOCOM) put the two to the test to see how they stacked up against each other. The purpose of the testing was to compare which system was superior in regard to repeatability, endurance, rough handling, drop testing, and failure load.

V Slot Vs T Slot Odds

In the Endurance and Rough Handling tests, both systems passed. The most significant variation was in the Repeatability test. M-LOK came out on top with the least amount of MOA shift when removing, then reattaching, an accessory rail with a laser sight. They found that in a drop test, M-LOK accessories remained attached 100% of the time, while KeyMod accessories remained attached only 33% of the time. From this testing, the M-LOK was selected for use on the Suppressed Upper Receiver Group and Advanced Sniper Rifle programs.

While this testing did not fare so well for KeyMod, that does not necessarily mean that it isn’t a feasible option for applications outside of military use. Both mounting systems are readily available, though M-LOK is arguably more popular.

Both designs are functional, but for one reason or another, people are often to draw to one over the other. Whether you choose KeyMod or M-LOK, you’ll have a convenient way to mount accessories directly to your handguard.