Standard T Slot Dimensions

TypeAttachment System
Place of originUnited States
Production history
DesignerMagpul Industries
Magpul MOE handguard on a user-assembled AR-15 semi-automatic rifle

These plates have three T-slots for use with T-slot nuts, bolts, and setup studs. Fixturing Tables Add components such as clamps, brackets, stops, rests, mounting plates, fixturing squares, risers, and V-blocks to build fixtures for welding and assembly. Make T-Slots for Jigs, Fixtures, and Slatwalls! Offered in three popular sizes, these T-Slot router bits are handy for making slot walls for your shop that work with standard size bolts. Making custom fixtures or wall display units with these premium quality router bits has never been easier.

A STNGR USA 15 in (381 mm) HWK M-LOK handguard on an AR-15

M-LOK, standing for Modular Lock, is a free licensed[1]firearmrail interface system developed and patented by Magpul Industries.

Standard T Slot Dimensions Metric

M-LOK allows for direct accessory attachment onto the 'negative space' (hollow slot) mounting points, and is a competing standard to VLTOR's open sourcedKeyMod system for replacing the ubiquitous Picatinny rail in some applications.[2] Compared to the Picatinny rail system, both M-LOK and KeyMod enable the user to have a slimmer, lighter, smoother and more fenestratedhandguard/fore-end with accessories mounted only where needed, whereas a Picatinny handguards typically will have rail slots for its whole length resulting in a heavier and bulkier handguard with sharp edges and poorer barrel ventilation.

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.


A prototype of the MOE slot was revealed by Magpul in late 2007 together with their Masada Concept Rifle (which would later be known as the Adaptive Combat Rifle). The MOE slot system was released by Magpul in 2009 as a feature on their MOE handguards, and at the same time compatible accessories such as Picatinny rail sections, direct MOE mounted light mounts, grips, bipod studs, etc. were released.

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 MOE slot system uses a weld nut which has to be placed manually on the inside of the handguard before mounting, making the slot system unsuited for applications such as free-floating handguards. Also, depending on the accessory item, the spacing increments between the MOE slots were not small or uniform enough to adjust the desired placement of accessories.

Acknowledging shortcomings of the MOE systems, Magpul drafted M-LOK as a new and improved mounting standard which was released in 2014 replacing the existing MOE slot. 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. It was designed to work with both metal and polymer parts.

M110A1 SDMR featuring a Geissele M-LOK rail handguard

In 2016, Colt Canada developed and released the Modular Rail Rifle (MRR) that uses a monolithic upper receiver with the M-LOK attachment system.[3] In 2017, several companies produce M-LOK handguards as well as accessories like Picatinny rail strips, vertical foregrips, bipods, sling adaptors, and flashlight mounts.[4]

In 2017, a summary report of testing conducted by NSWC-Crane for USSOCOM indicated that, while comparable in endurance and rough handling testing, M-Lok greatly outperformed Keymod in repeatability, drop testing and failure load testing.[5]


While M-LOK is free licensed, it is not open source, and thus manufacturers must acquire a license from Magpul before making products using the M-LOK standard. Magpul claims this gives them more control in assuring that all M-LOK products are made to specifications ensuring compatibility. Program participation is open to any interested manufacturer.

Technical specifications[edit]

Rail specifications[edit]

The slot dimensions (used on handguards, etc.) are available on the web.[6] The slots provide metric 20 mm (0.79 in) length intervals, and accessories can be mounted either within a slot or bridging between slots, making it possible to adjust the position of accessories in smaller intervals than the length of the slot. The slots on an M-Lok handguard are approximately 32 mm (1.260 in) long and 7 mm (0.276 in) wide and space 8 mm (0.315 in) from each other. The radius of the corners is approximately 2.38 mm (0.094 in).[7][8][9]

Attachment specifications[edit]

The quarter-turn T-slot nuts have different torque specifications depending on the handguard material:

  • 4.0 N⋅m (35 lb⋅in) for attaching metal accessories to metal handguards.
  • 1.7 N⋅m (15 lb⋅in) for attaching polymer or metal accessories to polymer handguards.
  • 1.7 N⋅m (15 lb⋅in) for attaching polymer accessories to metal handguards.

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). Many M-LOK screws on the international market instead use either M4 or M5 metric threads to reduce cost.

The tool required for mounting, in addition to the thread size, also depends the screw head type. Hex keys are used extensively in the firearms industry, but metric and imperial hex keys as a general rule are not compatible. It is possible damage the tool and screw by selecting a tool that is too small for the fastener, which can be done by using an Imperial/customary tool on a metric fastener, or the converse. An exception to this is 4 mm hex keys, which are almost the exact same size as 532 in (3.97 mm). In many industries, this makes 4.0 mm (532 in) hex keys preferred for consumer products because end users can successfully use an imperial key on a metric fastener, and vice versa.

Hex key spanner (wrench) size

Thread type

Socket head
cap screw

• Button head cap
• Flat head counter-
sunk cap screw
M43 mm2.5 mm
M54 mm3 mm
#8-32 TPI9/64' (3.57 mm)3/32' (2.38 mm)
#10-24 TPI5/32' (3.97 mm)1/8' (3.18 mm)

While screw and slot dimensions are available on the web, the T-slot nut dimensions are currently under review by the US State Department to determine whether it should be regulated by ITAR, and until it is clarified drawings are only available to US citizens.

  • M-LOK handguard and attachment parts

  • M-LOK approximate slot dimensions. (Primary measurements in millimeters, inches in parenthesis).

See also[edit]

  • Rail Integration System, generic term for a system for attaching accessories to small firearms
  • Weaver rail mount, early system used for scope mounts, still has some popularity in the civilian market
  • Picatinny rail (MIL-STD-1913), improved and standardized version of the Weaver mount. Used for both for scope mounts, and for accessories (such as extra sling mounts, vertical grips, bipods etc.) Major popularity in the civilian market.
  • NATO Accessory Rail- further development from the MIL-STD-1913
  • UIT rail, an older standard used for mounting slings particularly on competition firearms
  • KeyMod - competing standard open standard design to M-LOK for mounting accessories
  • Zeiss rail, a ringless scope mounting standard


Wikimedia Commons has media related to M-LOK.
  1. ^'Magpul Industries - M-LOK'. Archived from the original on 4 December 2017. Retrieved 6 June 2016.
  2. ^KeyMod vs. M-Lok: The Next AR Rail Standard by Chris Baker, November, 19, 2014
  3. ^Colt Canada Modular Rail Rifle (MRR)
  4. ^M-LOK Outselling KeyMod about 3 to 1, 28 January 2016
  5. ^Details On The USSOCOM Sponsored KeyMod vs M-LOK Test Conducted at NSWC-Crane, 5 May 2017
  6. ^Magpul Industries - M-LOK DESCRIPTION AND FAQ DOCUMENT[permanent dead link]
  7. ^' - M-LOK 2015 FAQs'(PDF). Archived from the original(PDF) on 7 April 2019. Retrieved 7 April 2019.
  8. ^M-Lok dimensions
  9. ^Magpul M-LOK estimated dimensions
Retrieved from ''
  • Metric T Slot Aluminum Profiles
  • Connectors
  • Fasteners
  • Accessories

Standard T Slot Dimensions

  • Frame to Floor
  • Panel Accessories
  • CarboSix Carbon Fiber

With T-Slot Aluminum, you get more value than you ever would with welded steel. Need flexibility? You've got it with t-slot aluminum. Need Versatility? Extruded aluminum has that too. Strong in the hot or the cold, corrosion resistant, extruded aluminum has everything you need to get a project done quickly and efficiently. No need to paint or weld unlike steel parts. Get whatever you need built fast and strong with our metric series profiles of extruded aluminum framing.

The T-slot Extruded Aluminum Advantage

For thousands of years humans have been fabricating useful, pleasing furnishings and other structures for the home and workplace out of an impressive range of materials, including straw, mud, stone, wood, brick, iron, steel, and other metals of various sorts. But it is only within the last hundred years or so that aluminum the most abundant metal in the Earth's crust has been utilized in an ever-increasing number of day-to-day applications. Partly this is because a cost-effective process for extracting aluminum from bauxite ore was not perfected until about 1920.

So there is one great advantage of employing aluminum for structural design purposes: it is plentiful. Its other advantageous properties include strength, lightness, formability, high ductility, and excellent corrosion-resistance. The innate utilitarian value of those properties is vastly magnified when the metal is formed into T-slot aluminum extrusions.

In a nutshell, T-slot aluminum forms the basis of a framing system for creating three-dimensional structural assemblies made with a variety of extruded and fabricated aluminum parts. With this system, each length of extruded aluminum contains one or more T-shaped indentations, or slots, into which various attachments (with ends also shaped like a 'T'?) conveniently fit and can slide up and down as needed. This allows you to interconnect other T-slotted aluminum parts into even the most complex configurations without having to clamp and weld them together as you would have to do with steel components.

Here are a few of the key advantages of adopting T-slot aluminum solutions to meet your structural design needs.


True, steel is harder and 'stronger.' But by the same token, aluminum is among the lightest of metals used for modern engineering purposes, with a molecular density one-third that of steel. As a result, it possesses a strength-to-weight ratio that is actually superior to that of steel . Contrary to what you might think, extruded aluminum is strong enough to handle most structural design and assembly applications.

Once you factor in the inconvenience of moving and positioning heavy pieces of steel not to mention the added labor cost of welding or riveting them together, drilling and tapping holes for mounting bolts, and then cleaning, prepping, priming, and painting the surface of the metal then T-slot aluminum becomes an increasingly attractive option if you are seeking cost-effective structural framing solutions.


If it's tough enough for trucks, military combat vehicles, and commercial airliners, then rest assured that aluminum is tough enough for more prosaic, everyday purposes. One key aspect of this durability is its resistance to rusting. Rust is to steel as rot is to wood. Unlike steel, for all intents and purposes aluminum doesn't rust at all. A microscopic layer of oxide (which is responsible for the silvery-gray color of anodized aluminum) naturally forms on the surface of the metal and prevents that from happening. You don't even have to prime and paint it in order to protect it! If any of your project's aluminum extrusions or other parts never rust, then you'll never have to replace them saving you money and down-time in the long run.


Finally, one of the most important advantages to using T-slot aluminum extrusions and accessories is that, unlike permanently welded steel, the system is modular by design i.e., it is easily changeable. You can connect, position, and fasten together the aluminum profiles however you'd like, using the appropriate fasteners , connectors , and desired accessories . Later on, as needed, you can then adjust and rearrange them in any configuration you like.

The most common type of aluminum fastener used to fasten parts together is the T-nut: just drop it into the T-slot and then twist it into a locked position. That is so much easier than welding!

But where the real magic happens is in the versatility of our aluminum connectors. Just a partial list would include:

  • quick connectors
  • T-connectors
  • tilt connectors
  • milling connectors
  • bolt connectors
  • cube connectors
  • angle connectors
  • slotted gussets
  • corner brackets

Once you've put the finishing touches on the assembly with end caps, casters, cable blocks, machining jigs, tool hangers, cabinet siding, doors, or any of a number of other accessories that we carry, you're good to go!

For maximum versatility for both both our international and domestic customers, be aware that our T-slot aluminum extrusions come in both metric profiles and inch profiles .

From carts to aquarium stands , from shelves to enclosures , and from ergonomic workbenches to eye-catching signs , Framing Tech T-slot aluminum extrusion systems are designed, machined, and assembled for versatility—and they are built to last.

T-Slot Aluminum FAQs

  • What is T-slot Aluminum Extrusion?

    T-slot aluminum extrusion is a structural fabrication material that utilizes an engineered cross-sectional profile that is both strong and versatile in its use.

  • Will T-slot Aluminum Extrusion corrode?

    Our aluminum extrusion is non-corrosive. This is mostly due to the clear anodized finish that comes standard on all of our extrusion, but also due in part to aluminums natural ability to oxidize. The oxidation process creates a secondary layer of protection from corrosion, similar to how copper will patina.

  • Is T-slot Aluminum Extrusion considered a “Green” material?

    Yes! Due to excellent recycling practices most of the aluminum ever produced is still in use today. In fact, aluminum is 100% recyclable and of the most common materials recycled aluminum is the ONLY material that is infinitely recyclable. It is also much lighter than glass and steel per cubic inch, and has a much smaller carbon footprint during fabrication, processing, and shipping.

  • Why choose aluminum extrusion over steel?

    The main advantages are that aluminum extrusion is more versatile, modular, easier to work with, and costs less than steel. Stef craps ghent university. Building with aluminum extrusion is as simple as inserting a connector into the t-slot and tightening it into place with standard hand tools. No need to clamp, weld or paint aluminum extrusion. T-slot aluminum extrusion makes it easy to re-locate pieces or add onto your current structure at any time.

    What is aluminum extrusion used for?

    Currently, T-slot aluminum extrusion is widely used in automation, material handling, safety guarding, manufacturing and laboratory applications. However, many people are adopting t-slot aluminum extrusion for use in a wide variety of projects. Some have even built their own machines such as 3D Printers and CNC machines using our aluminum extrusion.

  • What is a T-slot, and how do I use it?

    A T-slot is what we call the channel that runs the length of our aluminum extrusion shapes. The T-slots are designed to a specific depth and width depending on the material. The T-slot is used mostly for mounting and fastening a wide variety of accessories and panels to the aluminum extrusion. Often, panels will be inserted into the T-slot to quickly create a wall or enclosure.